WIP: First stab at git post-commit hook

[floehopper]

The post-commit hook parses the state of the code after each commit to the master branch, builds a tree of method definition "files" using ri-style naming, and adds a corresponding commit to the orphan method-log branch.

• This code assumes the method-log branch already exists.

• I've not thought about what happens if the history on master is re-written.

• There is no explicit reference between the commits on master and those on the method-log branch.

• I'm not sure how tenable it is to use a Gemfile and bundler for this hook. Maybe an in-line Gemfile might be better.

• I've duplicated some code from elsewhere in the repo, e.g. #unindent.

• I've used instance_variable_get on the instance of MethodFinder, but it would be easy to surface this as a public attribute reader method.

[floehopper]

Note that the code in this branch is very similar to that in the recently added build_methods_repo script.

[floehopper]

Rebased against master and force-pushed.