[NUCLEO_F401RE] Remove PB_11 pin.
[NUCLEO_L152RE] Change us_ticker timer (32-bit one)
[NUCLEO_F401RE] Change us_ticker timer (32-bit one)

Remove also the disable/enable timer update IT in sleep (no more
necessary).
Merge pull request #177 from bcostm/master

Change us_ticker timer (32-bit) on Nucleo L152RE and F401RE
add arduino I2C naming to PinNames.h
workspace_tools: Add execution right to build scripts
workspace_tools/build.py: Check if given MCU and Toolchains are supported by the build system
libraries/USBSerial: Allow to create an instance without the USB cable being plugged in

Prior to this change the connection was waiting for a USB cable to be plugged in.
Merge pull request #178 from sg-/FRDM-fix

add arduino I2C naming to PinNames.h
Merge pull request #179 from oliviermartin/om/build-added-error-msg

Added error message to build.py
Merge pull request #180 from oliviermartin/om/usb-serial-non-blocking

libraries/USBSerial: Allow the USB connection to be non-blocking
Added checks on compilation flags.
Merge remote-tracking branch 'upstream/master'