A working h_drop_from which rewrites its underlying sequence as a sequence containing some ignored parsers.

Changed parser test macros so that _parse_ok just checks whether the match succeeded and _parse_match actually checks the resulting parse tree

Revert "C++ tests set up. They probably don't compile; need to write iostream ops for prettyprinting and set up C++ build in scons." Should have branched it.

This reverts commit 6a29277d.

C++ tests set up. They probably don't compile; need to write iostream ops for prettyprinting and set up C++ build in scons.