Add HTTPS library
Fixed some bugs in HTTPS library
Add support for calling a function before main()

The name of the function is mbed_main.
Fixes PRMBED-906.
[KL25Z] Restore full SPI pin mappings
Interrupt chaining: preliminary version
Interrupt chaining: now working on all targets.

Tested on LPC1768, LPC11U24, KL25Z, LPC2368.
Interrupt chaining: added documentation, fixed a synchronization issue in CallChain.
[KL25Z] Fix I2C issue related to the silicon errata.

Makes a difference when running the I2C EEPROM test at 400KHz, which has a 100%
success rate after this change.
Add test groups.

Group tests with the same functionality into groups that can be used by autotest.py.
The groups can be overriden from private_settings.py.
Add support for calling a function before main()

Also added a test for this feature (MBED_A22).
Fixes PRMBED-906.