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 hammer/hammer!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 hammer/hammer!18

Test/fix h_bits(0, ...)

See merge request hammer/hammer!17

fix string escaping in json output

See merge request hammer/hammer!15

Support custom pretty-printers with USER token types

See merge request hammer/hammer!14

add combinators h_skip, h_seek, h_tell

See merge request hammer/hammer!13

revert changes to examples/base64 - bad merge

See merge request hammer/hammer!12

add const to the pointer arg to h_make_bytes

See merge request hammer/hammer!11

Compiler fixes

See merge request hammer/hammer!10

also allow NULL argument for unamb_sub to mean default