libflux: add version byte to wire protocol
build: make a2x utility optional

Only build manpages if the a2x utility is found.
This makes a missing a2x binary a warning instead of a fatal error.

Continuous integration builds can now optionally forgo install of
the huge list of dependencies for asciidoc, which will allow better
turnaround time for quick tests.
test: spellcheck man page sources instead of generated files

There is no reason that spell check has to be done on generated files
instead of their asciidoc sources. In case manpages are not built,
check source *.adoc files instead during 'make check' so that we still
catch spelling errors.
travis: do not install asciidoc during travis-ci build
Merge pull request #111 from grondo/a2x-optional

make manual page generation optional part of build
libflux: rework message api

flux_msg_create () now takes one argument, the message type.

Instead of scanning and guessing, add a protocol flag to
indicate presence of routing delimiter, and routing accessors
to get/set the flag/delim and manipulate the stack of route
frames.

Treat payload and topic string like other message attributes
with get/set accessors.

Add functions for matching topic strings in place (no malloc).

Expand unit tests.
libflux: request.c use new message API

minimal changes to get things working
api: use new message API

minimal changes to get things working
broker: use new message API

minimal changes to get things working
libflux: rename route enable/disable etc

Rename FLUX_MSGFLAG_RTE to FLUX_MSGFLAG_ROUTE
Rename flux_msg_set_rte (zmsg, true) to flux_msg_enable_route(zmsg)
Rename flux_msg_set_rte (zmsg, false) to flux_msg_clear_route(zmsg)
Eliminate flux_msg_get_rte.

Ensure that route accesors do the right thing with an empty
route stack (set id to NULL) and with a message that has no route
delim (EPROTO).

Add inline comments for routing functions in message.h and update
unit tests.
libflux: request.c update use of renamed route functions
api: update use of renamed route functions
broker: update use of renamed route functions
libflux: inline doc comment on payload functions
Merge pull request #113 from garlick/message-api-rework

Wire protocol and message API improvements