Removed test and doc from target all in Makefile

[jfacorro]

When running tests with erlang.mk and using meck as a test dependency, all of meck's tests are always run before the project's, which consumes some considerable time when running tests. This is due to the fact that erlang.mk executes make for each dependency when building the tests and the all target in the meck's Makefile includes the target test.

[eproxus]

Can you also change the README.md so that the instructions for running the tests are correct? Also please add instructions for building the documentation separately.

[jfacorro]

@eproxus I've updated the README to indicate how to run the tests and generate de documentation. Please let me know if you think there'a anything else missing or that can be improved.

[eproxus]

Looks good.