Fix bug in `count_lines_by_speaker` method

`count_lines_by_speaker` is now looking for exact match in speaker's
name.

Example XML:

<SPEECH>
  <SPEAKER>A</SPEAKER>
  <LINE>Line!</LINE>
</SPEECH>
<SPEECH>
  <SPEAKER>AAA</SPEAKER>
  <LINE>Line!</LINE>
</SPEECH>

before:
count_lines_by_speaker('A') == 2

now:
count_lines_by_speaker('A') == 1
Update output.txt (for MACBETH)