Also add ASCII art to illustrate definitions and layout.

See #103.

Also add ASCII art to illustrate definitions and layout.

See #103.

We need to control the y-axis line and label locations for each panel
in order to support a log y-axis in a panel.

See #103.

The yaxis_expr() function captured the first argument as an expression
and substituted that argument symbol into the y-axis expression to
render. This was more complicated than necessary.

Put all the logic into one single expression, instead of building
multiple expressions and concatenating them together based on arguments
to new_panel(). This required adding 'use_get_ylim', 'draw_left_yaxis',
and 'draw_right_axis' into the panel environment.

Adding 'use_get_ylim' to the panel environment means get_ylim() is only
called once. This improves performance because each call to get_ylim()
calls update_panels().

See #103.

These values are the same for every point the function is called.

See #103.

Multi-panel plots were the only time 'use_get_ylim' was TRUE. And the
only time it had any effect was when 'is_ylim_fixed' was also FALSE,
which was only true when 'yaxis.same' was TRUE.

This was one of two times we had to re-calculate the 'ylim' based on
every panel. The other time was when 'ylim' is NULL and 'multi.panel'
was FALSE. And 'is_ylim_fixed' is also FALSE in that case, so we know
to re-calculate 'ylim' whenever 'is_ylim_fixed' is FALSE.

See #103.

It's hard for me to reason about doing something different when a
boolean is FALSE. It's easier to reason about doing something different
when the boolean is TRUE.

Rename 'is_ylim_fixed' to 'use_global_ylim' and reverse the logic so we
recalculate ylim when 'use_global_ylim' is TRUE.

See #103.

This creates y-axis labels using the raw series values, instead of the
log series values. So the labels and locations are in round values of
the raw series, but rendered at the logged locations.

See #103.

# xts 0.14.x (202x-xx-xx)

* `plot.xts()` now renders all panels when 'x' has more than 8 columns and
  `multi.panel = TRUE`. Columns 9 and later didn't render because the default
  of `plot.xts()` is 'col = 1:8'. Thanks to Ethan Smith for the report and
  patch.
  ([#423](joshuaulrich/xts#423))
  ([#424](joshuaulrich/xts#424))

* `plot.xts()` no longer errors when 'ylim' is constant and negative. Thanks
  to Ethan Smith for the report.
  ([#422](joshuaulrich/xts#422))

* Do not use `SET_TYPEOF()` in C because it is not part of the public R API.

* `merge.xts()` no longer converts 'x' or 'y' from double to integer in the C
  code when they are not used in the result. This avoids an unnecessary and
  confusing warning. Thanks to Jeff Ryan for the report.

# xts 0.14.0 (2024-06-05)

* `addEventLines()` and `addLegend()` now draw on multiple panels when `on` is
  a vector. Thanks to Ethan Smith for the report.
  ([#420](joshuaulrich/xts#420))

* Replace `SET_TYPEOF()` in merge.c because it will error when it tries to
  convert a REAL to an INTEGER. Thanks to Kurt Hornik for the report!
  ([#419](joshuaulrich/xts#419))

* Fix crash when 'j' is not an integer and in [0, 1) (e.g. `j = 0.1`). Also
  throw a warning when 'j' is not an integer.
  ([#413](joshuaulrich/xts#413))
  ([#415](joshuaulrich/xts#415))

* Fix plot header when `layout()` is used to draw multiple plots on a single
  device. Thanks to Dirk Eddelbuettel for the report and testing!
  ([#412](joshuaulrich/xts#412))

* Fix plot legend location when the y-axis is log scale.
  ([#407](joshuaulrich/xts#407))

# xts 0.13.2 (2024-01-21)

* Print a message when `period.apply()` is called with `FUN = mean` because it
  calculates the mean for each column, not all the data in the subset like it
  does for all other functions. The message says to use `FUN = colMeans` for
  current behavior and `FUN = function(x) mean(x)` to calculate the mean for
  all the data. This information is also included in the help files. The option
  `xts.message.period.apply.mean = FALSE` suppresses the message.
  ([#124](joshuaulrich/xts#124))

* Fix error when `print.xts()` is called 'quote' or 'right' arguments.
  ([#401](joshuaulrich/xts#401))

* Fix `addPolygon()` so it renders when `observation.based = TRUE`.
  ([#403](joshuaulrich/xts#403))

* Print trailing zeros for index value with fractional seconds, so every index
  value has the same number of characters.
  ([#404](joshuaulrich/xts#404))

* Add ability to log scale the y-axis in `plot.xts()`.
  ([#103](joshuaulrich/xts#103))

* Actually change the underlying index values when 'tclass' is changed from a
  class with a timezone (e.g. POSIXct) to one without a timezone (e.g. Date).
  Add a warning when this happens, with a global option to always suppress the
  warning.
  ([#311](joshuaulrich/xts#311)).

* Significantly refactor the internals of `plot.xts()`.
  ([#408](joshuaulrich/xts#408))