Token tweaks

See merge request hammer/hammer!31

avoid a segfault when h_act_flatten() is called on a null token

See merge request hammer/hammer!29

differantiate error codes from h_compile() and update documentation

See merge request hammer/hammer!28

remove -Wno-clobbered from CFLAGS

See merge request hammer/hammer!27

this omission has nagged me a number of times and i think it must have been a
simple oversight.

this way the assert will fire from the user's code rather than the one in
glue.c:h_seq_index() which is not informative without a stack trace.

also includes commented-out tests for functionality that i discovered we never
provided, namely position and length information at the granularity of
HParsedTokens. at the moment, these fields always seem to be 0. we should
probably fix that or get rid of them. in the latter case it might make sense
to move this information to HParseResult, so the user can get access to it via
h_action() as needed.

the regex backend already returned 2 for an internal failure, contrary to
documentation, so this mainly brings the latter in line with existing behavior.

at the same time, fix a bug: h_compile would previously return "false" (0) on
exceptions (longjmp).

make use of our new freedom to signal different error conditions from the
context-free backends, notably "incompatible combinator" vs. "unresolvable
conflict".

it breaks the build with clang.

Fix pointer signedness warning in h_literal()

See merge request hammer/hammer!26

Unroll djbhash for ~25% speedup

See merge request hammer/hammer!24

Hammer arena malloc speedup

See merge request hammer/hammer!23

Hammer speedup

See merge request hammer/hammer!22

Provide an alternate interface to the arena allocator to avoid wasting time on unnecessary calls to memset()

Eliminate unnecessary hash computations in the packrat backend (roughly 2.5x speed in one benchmark)

Hammer gprof

See merge request hammer/hammer!21

Support --gprof build flag

See merge request hammer/hammer!20

h_drop_from

See merge request !19

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

enable h_repeat_n() for CF backends

See merge request !18

Test/fix h_bits(0, ...)

See merge request !17