Handling tags with empty values

[holub008]

Resolves: #62

Implementation: By making the space after a tag optional in the line PATTERN, content of '' will be extracted for the line, rather than failing to match the line pattern and concatenating the entire line to the current tag's content.

Testing: In addition to the test cases, I ran this change against my company's internal test suite for file import and saw no regression. Linter passes.