Make fails on Mac (10.11)

[Phil Allen]

`objecthash.c:2:10: fatal error: 'json-c/json.h' file not found

include <json-c/json.h>

     ^

1 error generated.
make: *** [libobjecthash.so] Error 1`

Cannot see anything in Makefile that would fetch this dependency.

[Glenn Rempe]

+1 I had a bad time trying to get Make to work on OS X. I never did get it to work and had to comment out all of the C compilation from the Makefile.

Instructions (+1 for getting dependencies with homebrew) would be awesome.

[Ben Laurie]

Partially addressed by 58616ff#diff-04c6e90faac2675aa89e2176d2eec7d8

[Tony Arcieri]

As soon as the build works on Mac we can add it to the operating systems Travis CI tests against in #37

[Ben Laurie]

It does work, except for Java, which I have commented out...