Save match data in change hook
Move custom variable to proper place

Also fix version indicator
Refactor Google This usage

As `google-string` is autoloadable in recent Google This versions,
just check it is `fbound`  instead of trying to require the feature.

Wrap the use of the function into an if expression, so that the byte
compiler recognizes the conditional use of the function and does not
emit a warning anymore.
Simplify argument substitution

Get rid of the helper functions, and use a single big pattern matching
case.
Add missing tests for substitution
Fix test cases

Regression from 807b8f7
Use `locate-dominating-file` instead of own code
[Fix #133] Make configuration file search customizable

Tests now depend against mocker.el, to mock hooks in tests for config
file substitution.
Slightly improve documentation

[ci skip]
Improve docstrings
Find configuration files in Projectile projects

Projectile is a cool project interaction library by @bbatsov.  See
https://github.com/bbatsov/projectile.