added json parser with base handler and exception, and tests -- no UTF-8 validation or Unicode escapes
fixed bug in parser, added more unit tests
more unit tests, fixed parser bugs, added error messages
unit tests for strings, bugs fix
more unit tests, better parser diagnostics, added json.hpp
json data handler and unit tests
unit tests for json_data_handler
command reads data in JSON format, added more checks, tests, to json_data
parser handles unicode escapes, checks for number range errors, more unit tests
reverted command.hpp to use io::dump
removed spurious comments
added class-level doc
correcting unit test
Merge pull request #618 from stan-dev/feature/issue-595-json

Fixes #595. Feature/issue 595 json