FIX: Check speaker_info is populated before pulling values from it
FIX: Reference correct local variable for mute value
FIX: Properly check bass & treble arguments for False

Previously, we did `if bass:` which wouldn't function correctly if the
developer did `soco.bass(0)` (set the bass to 0), since the 0 value
would be interpreted as False rather than 0.
Clarify documentation for `set_play_mode`
FIX: Import the re package when needed in `get_speakers_info`
FIX: Correct minor typo in method list