v2.0.0

This is primarily a modernization release, and contains some relatively small backwards incompatible changes.

• Track rhythms can now have spaces in them. For example, X... .... X... .... is now a valid rhythm. Spaces are ignored, and don't affect the rhythm. For example, X... X... is treated as the same rhythm as X...X...
• Wave files using WAVEFORMATEXTENSIBLE format can now be used, due to upgrading the WaveFile gem dependency to v0.8.1 behind the scenes.
• Installing the gem is now simpler, since it no longer requires installing the legacy syck YAML parser via an extension.
• A Fixnum is deprecated message is no longer shown when using Ruby 2.4
• Backwards incompatible changes:
  • Song files containing a Structure section are no longer supported. A Flow section should be used instead. Support for the Structure section has been deprecated since v1.2.1 (released in 2011).
  • Track rhythms can no longer start with a | character. For example, |X...X... is no longer a valid rhythm. However, bar lines are still allowed to appear elsewhere in the rhythm. For example, X...X...|X...X...| is a valid rhythm. The reason for this change is that a rhythm starting with | is parsed as a YAML scalar block now that Beats is using the Psych YAML library behind the scenes. The fact that the old Syck YAML library didn't treat rhythms starting with a | as a YAML scalar block appears to have been a bug in Syck?
• The minimum supported Ruby version is now 1.9.3, instead of 1.8.7