add lexical parser for headers

add lexical parser for headers

Profiling what happens during the ab test, one of the hotspots
was strcasecmp in a loop looking for header name matches each time.

This patch introduces a lexical parser that creates a state machine
in 276 bytes that encodes all the known header names.  The fsm is
walked bytewise as chaacters come in... most states do not need any
recursion to match or fail.

The state machine output is cut-and-pasted into parsers.c as an
unsigned char array.

The fsm generator is a bit rough and ready, included in the tree but
not built since normal mortals won't need to touch it.

Signed-off-by: Andy Green <andy.green@linaro.org>