Improvements to requesting backend by name pulled out of the dlopen spike branch

See merge request PicoMeg/hammer!1

spike branch: parsing of more complex backend requested parameters
string, with optional paramaters, etc. formatting of code fixed, unused
string based parsing of request parameters removed, etc.

backends[backend]

right now there is duplication as the enum backend value is still
present- need to find out if it's OK to make a breaking change for
anyone who is for reasons known only to themselves chekcing which
backend enum value is one a parser they may have created and compiled...

vtable pointer, clean up some of the redundant information in backend
with params struct

HParserBackendWithParams

compared to with strnig functions. WIP, feedback requested

better_backend_handling

but ready for review

committing now because of harddrive making a bad sound again.

cleanup

hard drive sounded bad. TODO includes free and copy updated and a bunch
of refactoring / redesign of the solution

Add ABNF-parser-derived bug60 test case, and improve some of the test macros

See merge request hammer/hammer!45

Ticket 60 bugfix

See merge request hammer/hammer!43

"glr(1)" and call compile for the appropriate backend. Needs clean up
and refactor, and tests, but it compiles and my hard-drive is
periodically making threatening noises...

better_backend_handling

Conflicts resolved:
	src/SConscript
	src/test_suite.h

that we also check to confirm both engines have consume the same number
of tokens (and thus have actually both arrived at the same state for the
same partial input stream)

Fix uninitialized symbol warning in cfgrammar.c

See merge request hammer/hammer!42

Fix feature macros

See merge request hammer/hammer!41

Restore -D_POSIX_C_SOURCE=200809L in build flags on Linux; we'll figure out report of Mac OS breakage later

Using _POSIX_C_SOURCE in the middle of a header is incorrect and may work unreliably because of multiple-include guards

add regression test for issue 87 - same as issue 91

Closes #87

See merge request hammer/hammer!37