Fix for latest (2.4.0) ESP-Arduino version

Board.txt contents changed in latest versions and this broke a reg
exp matching for LWIP variant.
Changed build state trigger to do a full clean build.

Fixed board handling for esp32

Some problems with board specific flash size etc, affecting
all esp32 boards, have now been fixed

Added support for LwIP

It is now possible to select which variant of the LwIP library
that should be used during the build (when applicable)
Controlled via the variable LWIP_VARIANT and the value should
be set to the corresponding value in boards.txt. Current values are:
open, Prebuilt, Espressif, OpenSource

CUSTOM_LIBS added. Build problems fixed.

Added new variable CUSTOM_LIBS which can be used to emable
automatic scan for libraries outside of esp and Arduino libs

Fixed build problems due to new format in boards.txt in latest
version of esp8266/Arduino

Fixed error in state version handling

Mac OSX problems fixed

Improved state check

Filesystem ota added

Added new rules for
  File system update via ota
  Complete flash erase
Corrected dependencies for file system generation
Fixed case bug for ARDUINO_ARCH_ macro
Readme updated
Progress bar now shown during ota operations

dump_fs added

New option to extract the whole file system from the flash

Use esptool.py also for esp8266 when available

Added LD_EXTRA