Add failing test for first column matches

word_column finds too many words when initial word is in the first
column. Right now, it often selects the whole file. Add failing test to
demonstrate this bad behavior.

Start of line test fails.
End of line test passes.
Fix start of line test: don't select everything

Instead of always accepting first/last column, change the pattern we use
to not require a preceding char (like we're accepting start of line as
the preceding char).

Change end of line to match (this doesn't seem necessary, but it works).

All tests pass.