Add support for custom options.

According to the Protocol Buffers Language Guide [1], custom options may be specified by wrapping the name in parentheses.

[1]: https://developers.google.com/protocol-buffers/docs/proto#options
Merge branch 'add-support-for-custom-options' of https://github.com/eventualbuddha/node-proto2json into eventualbuddha-add-support-for-custom-options

Conflicts:
	lib/parser.js