Replacement for fw_meta.py commands and also supports unbundling .hex files.

General syntax is:

```
 $ mos create-fw-bundle -o fw.zip part1:prop1=val1,prop2=val2,... part2:...
```

Example of building a mos fw bundle for ESP8266:
```
 $ mos create-fw-bundle -o fw.zip --platform esp8266 --build-info=build_info.json \
    boot:addr=0x0,src=rboot.bin,update=false \
    boot_cfg:addr=0x7000,size=0x1000,fill=0xff \
    fw:addr=0x100000,src=demo-c.bin \
    fs:src=fs.bin,type=fs,addr=0x8000,fs_size=262144,fs_block_size=4096,fs_page_size=256,fs_erase_size=4096
```

Example of converting a HEX file to a bundle:
```
 $ mos create-fw-bundle -o fw.zip host:type=host,src=hostfw.hex
```

CL: mos: Add create-fw-bundle command

PUBLISHED_FROM=35f52ea53e4b5900463415257323a4c08cf45deb

PUBLISHED_FROM=0cf3029d9a9b851882325e2298b878bc83fc2d33

Go back to Ubuntu 16.04 and older gcc-arm (4.9.3).

Boot loader just won't run when compiled with newer GCC (7.x).
It's likely that it can be fixed with compile switches but I couldn't figure it out quickly, so going to just downgrade for now to get it back to workign state.

CL: CC3200: Fix boot loader regression

PUBLISHED_FROM=b70b03bd17e03c7dae02328b32b855f3ca3ad6a9

CL: Add mgos_gpio_blink()

PUBLISHED_FROM=a5d2e2f44413d1ab363abeeaf0fb497bd8f63d6d

PUBLISHED_FROM=694346bd6562c55e5ab00886df47f7cbfb0a3720

mbedTLS is just another lib now

CL: Use mbedTLS from mongoose-os-libs/mbedtls

PUBLISHED_FROM=bae4739d22e871bd268b8a3233dbb69634770243

 * Update CubeL4 to 1.13.0
 * Rebuild OurTLS with `-DMBEDTLS_X509_CA_CHAIN_ON_DISK`
 * Add `-Wextra` and fix build issues

CL: Update STM32 build image

PUBLISHED_FROM=a7eacff7580bab6c6e40bdaf6164df575a717c55

CL: STM32: Make LWIP optional

PUBLISHED_FROM=eebffe7800a74d7b69aafd95e476b2e90328be98

 * Change return type of mg_mgr_poll to return number of events
 * Add mg_mgr_min_timer
 * Refactor main poll loop to remove LwIP-specific stuff

CL: Refactor mg polling

PUBLISHED_FROM=dc94618b32fa3c84a2f053bd04d134297780ec82

A smattering of other related changes

CL: STM32 OTA support for L475-IOT01 and DISCO-F746

PUBLISHED_FROM=e7142337086d09ba21437455b22d00db47ab33f1

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

PUBLISHED_FROM=0998fad82fbcdbde30dca42833f2e48d148592bf

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