Implement inlineSourceMaps option.

Add sourceMapURL method to Compiler, call btoa when option is set.
Override in NodeCompiler with node version.
Add test for node option --inline-source-maps.
Verify browser via repl.

Based on suggestions by @jeanlauliac and @guybedford
Fixes #978 Fixes #892 Fixes #1393
Note this encoding solution isn't correct, as it will change non-standard characters I'm using it in the module loader because we can't include a custom base64 encoding solution due to filesize constraints, but in Traceur it is probably worth using Buffer like in http://stackoverflow.com/questions/6182315/how-to-do-base64-encoding-in-node-js.