Add tests for TAP plans appearing at the end
Add init and fini methods to kyua_tap_summary_t

These are to allow the caller to manage the lifecycle of the object,
which we will need to hold dynamic strings within the result.
Implement support for TAP skip plans

TAP test programs can provide a "skip plan" to indicate that the whole
program is being skipped regardless of what its tests do.

Fixes #86.
Report passed tests that exit non-zero as broken

Fixes #92.
Handle lines that look like results but aren't

Lines containing "ok" and "not ok" only are supposed to be ignored.
To fix this, add some fancier parsing for the results so that we
only recognize ok/not ok lines if they also contain the corresponding
numerical identifier of the test.
Merge branch 'fix-tap'

The work in this branch is inspired by the contents of a pull request
previously submitted by Garrett Cooper but that was discarded.

Fixes #86, #90 and #92.