Fix build error parsing and Haxe SDK configuration

Fix build error parsing to:
1) not prepend anything to paths that are already absolute.
2) parse the error column, if available
3) use the correct root directory to resolve relative paths when building with a NMML.

Also, fix Haxe SDK setup to:
1) parse stderr (rather than stdout) to get the version number
2) prefer the HAXE_STD_PATH, if set, to determine the path to the Haxe standard library
3) prefer the HAXE_DOC_PATH, if set, to determine the path to Haxe documentation.