Add tests that capture the failure state.
Remove failure expectation.
Replace defunct syntax with valid function definition syntax.
Tidy up a couple very long lines.
Make a test that is expected to fail actually fail.

`indents-last-commented-line' was passing unexpectedly. The example in
the test differs from the example given by
https://github.com/elixir-lang/emacs-elixir/issues/27. The latter does
cause the expected failure in the test.
Add expected result to all failures.
Capture specific grammar error around 'end' statement.
Fix typo in test that lead to false failure.
Remove expected failure statement.
Remove unnecessary newline
Use correct syntax highlighting for use/require/import
Add a SMIE rule function for "def" tokens.

This function now explicitly sets the indentation level of lines
beginning with "def" to 2. Formerly, this token returned `nil` (the
default, because there was no matching pattern in `elixir-smie-rules`),
which caused SMIE to call `smie-indent-after-keyword` to calculate the
indentation. This function was returning the incorrect value which was
causing the inappropriate alignment to the `.`.
Some code cleanup.