fixes #264 panic in req (#265)

Go 1.13 is too old.

We need to test with more recent Go versions on Windows and
Darwin.  Additionally, we really would like to matrix test
things on Linux (which runs faster because of more resources
that are available) across a matrix of Go versions.

The matrix currently includes Go 1.13 through Go 1.18.  At
some point in the near future we will be pruning back on
support commitments for older Go versions.

Minor fixes to formatting, grammar, and spelling.

Corrected omission of Eritrea from the list of Russian supporters.

Update documentation links, convert README to markdown.

While ASCIIDOC is richer, it isn't as widely supported.
Additionally, the image used for mangos previously is not
one we have ownership for, so we feel best to drop it.
(We will follow up with a proper logo later.)

failNoPeers context support.

fixes #224 Desire FastSendFailNoPeer option

Shut up codecov (thanks for breaking paths codecov!)

Fix compilation errors in 3.1.1 on Windows.

Make IPC option symbols available everywhere.

This reduces some friction when using these options in
code that may be built for different platforms.

fixes #213 Want options to set permissions on IPC socket

This adds new options only available on UNIX systems to set
the permissions and ownership of the UNIX domain socket.
It also adds fixes to work better when testing with WSL
by forcing the sockets to be created in a temp dir.