Bump version for minor release
example: Print code as well as example
example: Use coffins to typeset side-by-side

Uses coffins to typeset the code side-by-side with the example. The
styling is still a bit quirky, as is the code (and undocumented),
with a dumb line separating the two parts that may not look very good.
Might have to colour  and fine-tune it a little.
\skdoc@verbatim: Hide line numbers when inside example
Replace toggles with l3prg booleans

Fixes an unreported bug in the 1.2-branch code that made examples not
print code at all. Also cleans up \skdoc@verbatim a little, as per #5.

References #5.
example: Fixed spacing, center vertically

References #5.
Documentation: document the example environment

Also fixes a few minor errors in the documentation.
\skdoc@verbatim: Documentation
Merge branch '1.2'

Merge the last feature to enter v1.2 and release. Update documentation.

Closes #9.