Ignore build dirs and resulting binary
Add an option to read avro schema from an external file.

In addition to the new -S <file> option, this commit adds more argument error handling,
much mroe detailed help information, memory stats feature flag help and a check that makes
sure memory stats are not executed on non-linux systems.
Merge pull request #5 from swiftype/external_schema

Add an option to read avro schema from an external file