Pin python dependencies to an API version, remove pyocd dependency (#158)

* Pin python dependencies to an API version

* Remove pyocd dependency.

Wherever pyocd is used, the imports are wrapped in try/except blocks
and an error code returned. It seems as though it is already and
optional dependency, so I'm removing the hard requirement.

Author: bridadan

setup.py

@@ -54,9 +54,8 @@ def read(fname):
       },
       install_requires=[
           "mbed-ls>=1.5.1,==1.*",
-          "six",
-          "pyserial",
-          "pyOCD!=0.13.0"
+          "six==1.*",
+          "pyserial==3.*"
       ],
       classifiers=[
           "Development Status :: 5 - Production/Stable",