Pymata

This release resolves issue 32, fixes an issue with data latches and provides general code cleanup.

Pip considers "a" in a version number as alpha so the version was bumped to 2.08. No changes from 2.07a other than the version number.

See the [changelog](https://github.com/MrYsLab/pymata-aio/blob/master/documentation/changelog.md) for details.

A check for the maximum number of pins was not being performed and an exception could potentially be thrown.

This is a minor change with no operational code changes

A new feature has been added. To use this feature you must use either FirmataPlus or FirmataPlusRB. The keep alive feature sends a periodic keepalive message to the arduino (the period length can be from 1 to 10 seconds and is configurable as a parameter in the new keep_alive method. The arduino expects to see the message within the period time frame, and if it does not, it resets itself.

Once keep_alive has been actuated, it can be turned off by specifying a period of zerio.