Creation of a common structure IDL

* Created common.avdl
* Added error GAException type
* Moved GAKeyValue to common.avdl
removed GAKeyValue from reads.avdl
Enhanced .gitignore with the gitignore CLI tool

* Added OS support for OS X, Windows, Linux
* Added editor support for emacs and Vim
* Added Travis CI support back in for .travis.yml file (taken out by Linux template)
updated with additional deps from https://github.com/alexholmes/avro-maven
add the "open for 3 days" requirement for merging
Update CONTRIBUTING.md
Merged github.com/ga4gh/schemas master branch

Conflicts:
	src/main/resources/avro/reads.avdl

Conflict was the GAKeyValue record which was moved to common.avdl
Merge pull request #58 from delagoya/common_structure_idl

Creation of a common structure IDL
Merge pull request #61 from delagoya/pom_enhance

Update the pom.xml file to have all maven-plugin features
Merge pull request #65 from dglazer/contributing

clarify the "3 days" requirement for merging
Merge pull request #59 from delagoya/gitignore_enhance

Enhanced .gitignore with the gitignore CLI tool