v2.0.0-alpha.28

Bug fixes:

• Fix protoc error message "Plugin output is unparseable" for certain
  plugin output sizes, see #134.
  Thanks to @fenos for the investigation and fix!

New features:

• Add oneof accessor / mutator functions, see #129

Cleanup:

• Rename plugin parameters to "plugin options".
  The code generator request only accepts a single parameter string,
  but this should be considered an implementation detail. protoc
  uses --ts_opt, so we should speak of options, not parameters.