Add support for ending statements on a newline

[nilium]

This adds a bitflag to the parser to enable parsing newlines as
statement sentinels in place of semicolons. Semicolons continue to
work.

This still needs work to support a backslash before EOL as a means of
ending a statement, but since there's no lookahead on tokens right now,
that's a little tricky. Might be doable by checking if the last element
of the current statement is a '\' word.

Also, as-is, this requires that opening braces be on the same line as
the section they open. I don't see any reason to change this, so it'll
probably stick even if/when I add backslash line continuations.

[codecov]

Codecov Report

Merging #20 into master will decrease coverage by 0.06%.
The diff coverage is 90%.

@@ Coverage Diff @@## master #20 +/- ##
==========================================
- Coverage 90.43% 90.36% -0.07% 
==========================================
Files 4 4 Lines 1254 1277 +23 ==========================================
+ Hits 1134 1154 +20 - Misses 106 108 +2 - Partials 14 15 +1

Impacted Files	Coverage Δ
parser.go	91.7% <90%> (-0.51%)	⬇️

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