Fixes source map generating (#586)
Adds json library by Joseph A. Adams
Windows: Add guard for snprintf.
Also fixes the warning for unsigned char*.
Adds base 64 encoding library

http://sourceforge.net/projects/libb64
Adds `add_source` helper function
Implements source map embedding

- embed sources content inside source map
- embed source map inside sourceMappingURL
Excludes external libraries from code coverage

They provide far more code than we actually use.
And we certainly don't want to test all that code!
Reverts back to using longhand options in travi-ci!
Fixes some minor clang warnings in sass.cpp.
Merge pull request #591 from mgreter/source-map-sources

[WIP] Implements embedding source contents in source maps
Fixes rendering of warn and debug statement
Allow \ in identifiers
Don't error when blocks terminated by ;
Merge pull request #608 from xzyfer/fix/issue_595

Don't error when blocks terminated by ;
Merge pull request #607 from xzyfer/fix/issue_502

Allow \ in identifiers
install newly required header in autotools build system

sass_interface.h #includes sass2scss.h so we need to have the
latter header wherever we have the former one.
Merge pull request #609 from idupree/autotools-header-install-fix

install newly required header in autotools build system
Fixes and improves travis ci build

Changes -std=c++11 to -std=c++0x!
Merge pull request #606 from sass/test/travis-ci

[WIP] Fixes and improves travis ci build
Removes redundant builds in travis-ci config

Further speeds up day by day travis-ci builds
This will still catch all coding errors!
Support function and mixin calls with both variable and keyword args
Reevaluate var and keyword arg flags after eval a \$variable argument

```
foo($bar...);
```

Will flag `$bar` as a variable arg when in fact it may be a keyword
arg. We can only be sure once `$bar` has been evaluated. If `$bar`
is evaluated to a map then it's a keyword argument and the
Argument object needs to be updated accordingly.