Refactor annotation parser

After #27, the old parse_annotation method was dead code
nowhere used. This commit removes the dead part and renames
the new method to the previous name, as it makes more sense
and specs point to it.
Add new annotation format as input for spec
Add missing space to annotation matcher

There is 1 additional space in the annotation format between
the line number element and the parsed line. Without this,
the output in the HTML popup for the blame indents 1 space to the
right.
Add spec for new behaviour of annotation parser