PUBLISHED_FROM=7864ffa26cb553f5d4a93248f67c288327ec23b0

Also fixed a memory leak on reconnect: previously, each reconnect was
creating a `struct mg_connection` which was never reclaimed

PUBLISHED_FROM=eefdcf557e032ac81d5ed3aba55ac912e400148e

PUBLISHED_FROM=0454cdeec5c7120eb4bf905fdd5b7abdcb4003c2

Currently only OpenSSL API impl, but the plan is to add more.

PUBLISHED_FROM=c85b26fa2312047768bdcf3eca583e60862aba90

PUBLISHED_FROM=46496c2d5340a0bbe4fe1c6c9ff187bc65d2d35f

Possible values:
  MG_NET_IF_SOCKET (1) - traditional BSD socket API
  MG_NET_IF_SIMPLELINK (2) - TI's SimpleLink socket interface
  MG_NET_IF_LWIP_LOW_LEVEL - a net_if implementation that uses LWIP's
    low-level API, when LWIP_SOCKET is not available.

PUBLISHED_FROM=a5c0aebb7b6bdb1f1f4cb3210763d16f3ab5e133

"#if FOO" still works with simple -DFOO, but gives more flexibility.
Specifically, if user expressed no preference (FOO is not defined),
we can apply reasonable defaults (this is the legitimate use of ifdef).

In short, from now on, please use

 #if MG_ENABLE_FOO

instead of

 #ifdef MG_ENABLE_FOO

Since we are all used to #ifdef, this change also adds a precommit check
to police this. Specifically, in *.h and *.c files that are Copyright Cesanta,
"ifdef" and "if defined()" are not allowed to be used with macros that contain
ENABLE or DISABLE, unless the like also contains "ifdef-ok".

Hence, if you are sure you want to use ifdef, use this:

 #ifdef MG_ENABLE_FOO /* ifdef-ok */

PUBLISHED_FROM=9be829448f53cff575d6cae8b9945fb12531c15a

PUBLISHED_FROM=293a54ab09e6879b6f0c36975a137eeaeff92098

SimpleLink sockets are suffciently different from BSD that all the
ifdefs have become too messy to warrant a separate net_if
implementation. As part of this we also implement proper async connect
support.

Added MG_F_SSL to identify SSL-enabled connections in a generic way,
since SSL state can be different depending on the implementation.

PUBLISHED_FROM=9cdb8c880b90683e4a26b972cf439d47d6f60917

SL requires cert and key to be separate files in DER format.

Date verification is disabled for now.

PUBLISHED_FROM=7d76150ed356140728a1e5fd82d8a0456347b7dc

It would be probably good idea to also remove tools/docgen.py and
asciidoc.mk, but asciidoc.mk is still mentioned under `cloud/doc`, which
may contain some useful info which we'll need at least to review before
removing.

PUBLISHED_FROM=faf454d4c52a2f07ea8ac084cf0bd11a0c9c9b3b

Until I read the doc and find how to limit the retention,
otherwise it just eats all my ram and cpu and things start to fall
apart.

PUBLISHED_FROM=eb33fb44736f07b992270689217aca4af70513ff

Comments in headers are changed a bit: removed adoc-specific stuff,
markdown is used instead

PUBLISHED_FROM=9242cce85cc52a47a197d377e7e23804721a6bb5