Exporting Natspec documentation to a JSON interface

- Adding a getDocumentation() function to solidity compiler stack
  so that we can obtain the natspec interface for a contract

- Adding libjsoncpp as a dependency of libsolidity. This is done
  in a dirty way, using libjsonrpc-cpp s an intermediate dependency
  for the moment. Will fix soon.

- Start of a test file for Natspec exporting to JSON
Using jsoncpp for exporting ABI interface from solidity

- Also changing the interface JSON test to have a shorter name
  plus to provide meaningful error message in case of failure
More Natspec JSON export tests and better error reporting
Handle absence of Natspec doc and add option to solc
Removing unneeded local variable in CompilerStack::getDocumentation()
Simplifying lambda function in CompilerStack::getInterface()
Separate user and dev natspec documentation

- plus other small changes according to the spec
Moving all Interface and Documentation functionality to own class

- Creating the Interface Handler class which will take care of the
  parsing of Natspec comments and of interfacing with and outputing to
  JSON files.

- Will also handle the ABI interface creation
Work in progress for parsing natspec doxytags
Styling in libsolidity's InterfaceHandler
Parsing notice and dev doxytags.

- Only initial work done. Still need to refine the logic and
  incorporate all the other types of tags.

- Added/Modified some tests

- Work in progress
Merge branch 'macos_build_fix' into build_enhancement
Natspec parsing @param doctags

- Plus additional work on generally parsing doctags.
  One important missing feature is to parse a tag midline

- Adding more tests
Merge branch 'develop' into natspec_export_json
Natspec @return tag parsing

- Also omitting tags from the output JSON file if they are missing
  instead of providing an empty string for their value
Addressing styling and miscellaneous issue with Natspec
Using iterators in Natspec comment parsing

- Used iterators in the entirety of the InterfaceHandler natspec comment
  parsing pipeline

- Fixed issue where @param continuing in new line would not get a space
Introducing Docstring parsing error exception and style fixes
Newline right after doctag is now a valid natspec entry

- Plus tests for that
Stack compiler now correctly returns a string and not a pointer