Rethink STM32 I2C v2 HAL (#78) ...

* Initial attempt at rethinking the STM32 I2C v2 HAL.  Makes single-byte work properly and adds a new 'state' variable to track what the hardware is doing.

* Fix some initial test failures

* Fix incorrect logic

* Fix more incorrect logic

* Tabs to spaces

* Fix repeated starts with single-byte API

* Fix race condition causing stop() after nacked address to sometimes break things

* Fix missed i2c structs that should have been removed

* Fix doing a repeated start from single-byte to transaction API causing I2C peripheral to lock up

* Fix xferOperation being set wrong for repeated starts, causing the peripheral to hang

* Fix race condition with repeated start after single-byte operation

* Fix compilation for targets that use I2C IP v1

* Fix initialization of XferOperation for API v1, optimize stop()

* Remove unneeded line

* Add docs for I2C events

- Split mbed-core and mbed-rtos into -sources and -flags targets ...

- Fix some logic errors in top level cmakelists related to building greentea tests
- Fix mbed_create_distro() for OBJECT libraries

Use standalone greentea-client ...

For CMake or Mbed CLI 2, use the standalone greentea-client.

CMake: Create mbed-greentea library

Tests: Remove support for ARM Compiler 5 ...

ARM Compiler 5 is no longer actively supported and was superseded in
Mbed OS by ARM Compiler 6.

Merge pull request #9561 from theotherjimmy/test-resources ...

Tools changes for bare metal

Remove outdated text and fix spelling in README.md ...

Remove reference to yotta, and fix spelling for correct branding.

Add placeholder libraries for things we probably refer to as libraries

Add a Unity macro to assert on platform error code difference

Unity: Add macros for test skipping. ...

The TEST_SKIP and TEST_SKIP_UNLESS macros (w/ and w/o messages) allow the test
to skip the test case execution from the point the macro was called (without
failing the test).

Unity framework : add float support in error print

Correct unity math for ARMC6 ...

The assumed that isnan and isinf would be macros, but they are functions
in ARMC6.

Add tags to our code

Adding test frameworks and test sources ...

This commit adds the following test frameworks:

- `greentea-client` (https://github.com/ARMmbed/greentea-client)
  - This framework provides a key-value api for communicating with the
    greentea test tool (https://github.com/ARMmbed/greentea)
- `unity` (https://github.com/ARMmbed/unity)
  - This framework provides test assert macros that can be used when
    writing test cases
- `utest` (https://github.com/ARMmbed/utest)
  - This framework allows you to execute a series of test cases with
    reporting that works with the greentea test tool
    (https://github.com/ARMmbed/greentea)

The following changes were made when bringing these frameworks into the
tree:

- References to `mbed_drivers/mbed.h` within utest's tests were migrated
  to `mbed.h`
- The yotta file `module.json` was removed from `greentea-client` and
  `unity`
  - `coverage.json` was also removed from `greentea-client`
- `.gitignore` and `.gitattributes` were removed from `greentea-client`
- Apache 2.0 license files were removed from `greentea-client`

This also brings in a number of tests that have been newly written or ported from various sources:

- `TESTS/integration` - Very basic tests, used to check if testing frameworks are working correctly
- `TESTS/mbed_drivers` (Thanks @PrzemekWirkus!) - TESTS ported from mbed OS 3.0 (https://github.com/ARMmbed/mbed-drivers)
- `TESTS/mbedmicro-mbed` (Thanks @PrzemekWirkus!) - Tests that weren't covered by `TESTS/mbed_drivers` that currently live in `libraries/tests/mbed`
- `TESTS/mbedmicro-rtos-mbed` (Thanks @PrzemekWirkus!) - Ported tests that currently live in `libraries/tests/rtos/mbed`
- `TESTS/storage_abstraction` (Thanks @rgrover!) - Tests for the storage_abstraction hal