CL: Make esp8266 compilation a little less verbose

PUBLISHED_FROM=0ec1412ea32243f263d52fbe0877ecca1efc5aef

Closes https://github.com/cesanta/mongoose/pull/945

CL: Fix build with CS_ENABLE_STDIO=0

PUBLISHED_FROM=7d15f17fc42241facdba5b1004b5b7f3dda599dc

CL: mos support for LFS (littlefs) https://github.com/ARMmbed/littlefs

PUBLISHED_FROM=e72957b4fb2c78949af4cf6d5bfef135ddba9fd9

Set CLOSE_IMMEDIATELY flag when destroying conn.
This avoid some races in LWIP adapter.

CL: mg_lwip: Fix race during clean conenction teardown

PUBLISHED_FROM=5c67982390dfaf83527e85d1291f64c6050aa932

startup cleanup on CC3220

CL: none

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PUBLISHED_FROM=9997c64ed0c713b5b8b29df7a49b532e880eac53

CL: Fix TZ on ESP8266

PUBLISHED_FROM=435a501a8b52524bccb67bb5a8ae7e09dfb4d44a

Also remove `-O3` optimization flasg, it negates `-Os`. Saves ~400 bytes.

CL: none

PUBLISHED_FROM=f40f42e4f54a8e0e003ab65ec8f5838c2d932876

CL: Apache license to common/

PUBLISHED_FROM=901e9e4b12a31289b3515d1f86dd56a7f0f35c5e

A major cleanup, disentangling net_if and ssl_if.
Pulled a lot of common logic into the core and reduced size of net_if implementations.

CL: Mongoose net_if and ssl_if refactoring

PUBLISHED_FROM=29bd4dcb264a1fd96b3dd164e2d880e1c2c0921e

In preparation for making moving to lib.
Reduce amount of makefile copypasta a bit.

CL: none

PUBLISHED_FROM=70a016491f9605e37708385bdd698f48a8d64119

PUBLISHED_FROM=78acb18d597b6f47f31da13087fa6685f21ce445