added support for google guice

[sdorra]

Hi, first of all thank you for the fantastic library. I've tried to use airline with google guice to create the commands, but guice fails because of a conflict with the Inject annotation of airline.

So i've build a module which populates the bindings of airline to google guice, so guice can be used to create the commands and handles the injection. But in order to implement the module, i've need to pass the context of the command to the CommandFactory for the creation. I know this is a breaking change, but is see a few options:

• accept the breaking change and schedule it for version 3 of airline
• turn the signature of the CommandFactory to a default method which calls the old signature for instantiation and calls the context for the injection (requires Java 8)
• create a new interface with extends the CommandFactory, adds the new signature and check with instanceof in the ParserUtil
• keep the old signature and populate the context over ThreadLocal

I've also had to add a dependency to jsr305 in order to support the null injection of CommandGroupMetadata.

[coveralls]

Pull Request Test Coverage Report for Build 381

• 76 of 77 (98.7%) changed or added relevant lines in 5 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.2%) to 75.069%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
airline-core/src/main/java/com/github/rvesse/airline/parser/DefaultCommandContext.java	31	32	96.88%
<!--	Total:	76	77	98.7%	-->

Files with Coverage Reduction	New Missed Lines	%
airline-core/src/main/java/com/github/rvesse/airline/parser/ParserUtil.java	1	68.75%
<!--	Total:	1		-->

Totals
Change from base Build 374:	0.2%
Covered Lines:	5471
Relevant Lines:	7288

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💛 - Coveralls

[rvesse]

Thanks, now merged. I've kicked off a deployment for the first 3.0.0-alpha-1-SNAPSHOT build so that should be available from the Sontatype OSS Repo in a little while.