Complete rewrite of the C Clubby implementation: it is now modeled after
the Go implementation, with a slight difference that codec and channel
are the same object (something we should probably do in Go as well, as
we only have a single type of channel so far, which is used with all
types of codecs).

This implementation also comes with a new external API,
which is hopefully cleaner and easier to use (see mg_clubby.h).

In this PR I am not adding any new types of channels, but a UART channel
as well as websocket listener channel will be added after this lands.

PUBLISHED_FROM=d545d4bb6434e2a02ad159f9e4b64e594a4797e7

PUBLISHED_FROM=20d24793d766ee289c6bde95bd5ad01202cd614b

PUBLISHED_FROM=fc3f24d40f92f206e5de4a2fd15100430db87717

PUBLISHED_FROM=8945dc72ce22d48c582e7cdd01348494677ac5bb

PUBLISHED_FROM=6bf2a710edaae6133d68eaf900ede14bba75ad5a

PUBLISHED_FROM=993c4b1bec363e3f7975b83710e694792bedf5b3

PUBLISHED_FROM=f85aaf2215f8323866eab9fb5143407b44fa1959

PUBLISHED_FROM=4eead54610606827963e7c244fcd8ab9a13d4c07

PUBLISHED_FROM=f1b4ce4334d24bf613db88ccb28cb3668390ce1d

PUBLISHED_FROM=6e33f546c4d096ef03103f6010124e5d568700b0

PUBLISHED_FROM=b2454104b99100f23db0777f874ab8a33727acca

A way to serve a single, specific file as opposed to the hairy monster
that is mg_serve_http.

PUBLISHED_FROM=6ed1bc487b9d41d212a5907337182f23b040aecf

PUBLISHED_FROM=03dc62aa69dddcbe41d5bc5c014de248332da918

PUBLISHED_FROM=c118b2796f697e8d5493bb3d534cee7406060c1a

Use templated index page and SSI calls instead of hard-coded html

PUBLISHED_FROM=eade9dfe283952ed5465cd0ff1924f61a14dea0c

PUBLISHED_FROM=5a24bda9029db3fc7bf04dc871656d65d551f4ab

PUBLISHED_FROM=243437cf7d48b04aef3896bc4c5d4010975299a4

PUBLISHED_FROM=542e7c82fa494bef52222495301ab53dce43cd8f

PUBLISHED_FROM=c6756bc74e6c25e4c120024e3ee2e3406068ad92

In CCS example projects

PUBLISHED_FROM=b3ab112f74ae475cb93bf06fdb7db811bbb99a59

PUBLISHED_FROM=7bacb1af60e85e4ed56a600fa3d1dbba1679db59

We haven't actually _fixed_ evaluation of precompiled bcode from
non-mmapped memory: we just never free it. For sane use case (do not
evaluate the same file more than once) it should be acceptable.

PUBLISHED_FROM=a9ca2d8fa72e9c40c93415d060ee8db697caa225

PUBLISHED_FROM=5cd78790a03580aa23dd3d2d8b825ad449083cc2

PUBLISHED_FROM=11c57fc5ece01686e9cecab5e3bfce54a2825836

PUBLISHED_FROM=8b7fcfc1bc32ff9ff38e2904ddb730c83bf9fae4