Implement `..`.

Now able to navigate ancestors using `..`. This is useful in sub-queries
where we might want to compare an array element to one of it's siblings,
or find the sibling following a particular array element.

Closes #27.
Merge branch `ancestors` into `master`.
Tidy `push`.
Build in FreeBSD.

Update `t/sizes` and `t/test` to work with a POSIX shell.
Escape special characters.

A path part is now entirely forward slash delimited so that white space
is significant. The backtick is the escape character.

The plan was to allow JSON strings as path parts, but that made for some
ugly path expressions. We're going to do this instead.

Closes #20.
Merge branch `escape` into `master`.
Fix select null and zero.

Closes #29.
Implement JSON pointer.

Closes #12.
Test that no dot is required in sub-queries.
Upgrade Proof to 0.0.20.
Add test and notes for parent operator.

Added a straight-forward test of the parent operator `..` and added
notes on the parent and self operators to `README.md`.
Apply self operator `.` to arrays.

The self operator `.` was not working correctly when applied to arrays.

Closes #31.
Use `in` operator instead of testing undefined.

Closes #30.
Upgrade Proof to 0.0.24.
Add `LICENSE`.
Add contribution guide.
Initial Coveralls build.
Run Coveralls coverage using actual tests.
Quite `t/cover`.
Upgrade Proof to 0.0.27.