Add a test for simultaneous device access

Add parallel_test.py to verify simultaneous device access is handled
correctly.

Merge pull request pyocd#264 from c1728p9/cmsis-svd_dependency

Make cmsis-svd optional

Merge pull request pyocd#240 from arekzaluski/ws-interface

Websocket interface

Merge pull request pyocd#235 from gamnes/master

Include support for nRF52 board ID 1101

Merge pull request pyocd#229 from c1728p9/pydapaccess_backport

Pydapaccess backport

Merge pull request pyocd#178 from c1728p9/fix_pyusb_install

Fix pyusb dependency