Check cache for valid .gitignore template name.

Update the cache and then validate against the cache, to ensure that the
template being requested exists.
Add clarification comments.
Fix a bug in the test regex.

Needs to be escaped to match a literal `.` character.
Currently matches any single character.
Extra comments for the gitignore service.

Update to the docstrings for the gitignore service.
Whitespace in a comment.
Extra information about merging headers.

Update the comments.
Networking comments.

Extra comments for the networking code and their docstrings.
Better client comments.

Not much, but an improvement on the old ones.