Implement Serialization Framework and rework WireFormat

[jhugard]

Implement Features from Issue #19

Needs final code review before merging to master.

• Rework WireFormat to support serialization
• Implement ZeroCopyBuffer to reduce memory copies and array allocations
• Create framework for serialization, with an eye to eventual F# code generation

Update: All of the above are now implemented, with unit tests.

Remaining work:

• For proto2, missing required fields should cause exception
• For proto2/proto3, need to elide default/zero values when serializing
• For proto2, missing optional messages should probably be modeled as a Some type

Would very much like a code review & feedback on the overall direction, in particular the serialization framework. Thanks!

[jhugard]

Ready for code review.

[ctaggart]

Great work!