Yotta is no longer supported by Mbed TLS, so has been removed. Specifically, the
following changes have been made:
 * references to yotta have been removed from the main readme and build
   instructions
 * the yotta module directory and build script has been removed
 * yotta has been removed from test scripts such as all.sh and check-names.sh
 * yotta has been removed from other files that that referenced it such as the
   doxyfile and the bn_mul.h header
 * yotta specific configurations and references have been removed from config.h

Made the use of 'Knowledge Base' consistent in the CONTRIBUTING.md and
README.md files.

Update the forum link in the readme file as well.

This clarifies that it's the string to type and not just some
description of it.

Change URL from developer.mbed.org to os.mbed.com

Change the Arm Trademarks according to updated Trademarks

* update README file

update VS 2010 as the minimal version of required Visual Studio

* Rephrase the MS VS requirement

Rephrase the VS version sentence

Our README claims that we only use basic Make functionality, but in
fact GNU make is required for conditional compilation. Document this.

Addresses issue #967

Our README claims that we only use basic Make functionality, but in
fact GNU make is required for conditional compilation. Document this.

Addresses issue #967

Removed an extra e from agreement.

Removed an extra e from agreement.

Update to contribution guidelines, some fixes in the language, minor
refinements and corrections.

For consistency