Empirical Bayes hooks

[ananth-pallaseni]

Added a new set of functions to plug into EmpiricalBayes. These are only loaded when EmpiricalBayes is found in the list of installed packages, else they are undefined. Added new tests for the new functions, also only run when EmpiricalBayes is found.

[Tchanders]

Thanks, this is really great. Reads well and is producing sensible results on real data.

In the absence of a detailed, PEP 8-type style guide for Julia, I've been aiming for keeping things internally consistent. So would you humour me with the following whitespace changes?

• change any consecutive newlines to a single newline (empirical_bayes_glue.jl and empirical_bayes_glue_tests.jl)
• indent with 4 spaces (empirical_bayes_glue.jl)
• put spaces either side of "=", including for keyword arguments (empirical_bayes_glue.jl) (Current consistency probably has room for improvement, e.g. spaces around colons and inside brackets, but at least keeping on top of the above is a start!)

I'm going to remove the patch coverage target.