…er (#1376)

This commit adds memoising singleton methods and switches to using
`Array#include?` to match against a set of keywords. This reduces memory
usage and allows for the keywords to be ordered alphabetically. Finally,
the `addrspacecast` keyword is added.

This commit adds a lexer for the FreeFEM language.

This commit adds a lexer for the GHC Core language.

The Console lexer would not correctly parse comments if only the
`comments` option was enabled. This was because of a bug in the way the
prompt's regular expression pattern worked. This commit fixes that bug
and adds a series of tests to confirm the behaviour of the lexer is as
intended.

The division operator was missing from the list of operators in the Rust
lexer. This commit adds the operator as well as some visual samples to
cover operator usage.

Rouge allows for options to be passed to a lexer's constructor method.
The options are parsed from strings and the string 'false' was not being
converted to the Boolean value `false`. This commit fixes that and also
adds a rudimentary series of tests to ensure that Boolean options are
being properly parsed.

This commit adds support for the `some` keyword and `\.Type.variable`
key-path syntax to the Swift lexer.

This commit allows for optional spaces after filter pipes in the Jinja lexer.

This commit adds a lexer for Objective-C++.

Since Ruby does not support multiple inheritance, the Objective-C rules
previously defined in the Objective-C lexer are factored out into a
common module that can be used by both lexers. Accordingly, this commit
also updates the Objective-C lexer to use this module.

As the common module uses memoised methods (e.g. `at_keywords`) that are
referred to within rules included in the common module, lexers that use
the common module need to use `Object#extend` rather than
`Module#include`. Consequently, the memoised methods are not prefixed
with `self` as would typically be the case. This is different to other
factored-out modules intended for reuse in lexers (e.g. the
`TypescriptCommon` module).

This commit improves support for comments in Jinja files. Previously,
multiline comments would contain error tokens if the commented text
contained the `{` character. This commit also adds support for
single-line comments.

Starlark is a dialect of Python that is used to configure the Bazel
build system. This adds file extensions to the Python lexer that are
used for files written in Starlark.