Add support for compiler option :inline-source-maps

Would like to see test status - Mike how are you dropping that in here? I can review after that.

Added patch #4 - remove forgotten printing of debug info.

Attached third patch.

Additionally I’ve done following changes (based on our discussion in #cljs-dev):

1. using url-path instead of util/path so we get consistent behaviour with forward slashes regardless of OS

2. wrapped cached-core in prepare-cached-core-if-needed and test :inline-source-maps there

3. added :inline-source-maps into build-affecting-options
   
   

Bellow is transcript of our conversation:

I would like to get this done. Can you please make the decision how to move forward? Thanks.

I looked into that windows build and sourceMappingURL in failed tests looks like this (note mixed slashes):

The problem is in existing code using util/path, which is OS-dependent and produces back slashes under Windows, my patch didn't modify that code branch:
https://github.com/clojure/clojurescript/blob/47386d7c03e6fc36dc4f0145bd62377802ac1c02/src/main/clojure/cljs/compiler.cljc#L1473

I guess we have two possible resolutions:
1. leave existing behavior as is and make my tests accept mixed slashes
2. newly use forward slashes only, leave my tests intact and announce it as a potentially breaking change in next release

Solution 2 is better way forward IMO. I believe mixed slashes work because browsers are forgiving and treat backslashes as forward slashes in source mapping resolution. This change would have some tiny chance of breaking existing code with would depend on specific way how clojurescript generated sourceMappingURL with backslashes up until now.

I will leave it for your consideration. And then move forward with your decision.