Introduce new options & lower required cmake version

  * Change CMake minimum required version from 2.8 to 2.0
  * Introduce VERBOSE & DEBUG options (both disabled by default)
  * BUILD_UNIVERSAL_LIB option now only appears if building in OSX
  * Re-include CPack; this feature was found in the original author's
build script (untested by me!)
Add License text
Introduce json_spirit find_package script
Introduce install targets for our license, readme & cmake module scripts
Rename cmake_uninstall.cmake.in to uninstall.cmake.in
Update comments
Re-enable std::map & std::unicode support
Rename BUILD_UNIVERSAL_LIB option to UNIVERSAL
Add Travis build script
Update README -- Add build instructions & changelog