Update to FPP v2.1.0a10

[bocchino]

• Addresses issue nasa/fpp#407
• Cleans up string code and corrects off-by-one error in buffer sizes
• Refactors code in Fw::StringBase that was terse and hard to understand (it was not clear what was going on with serializing and deserializing string lengths; because so much was implicit, it looked like the code was serializing and deserializing null-terminated strings).

Note: This PR will require some minor changes in user test code, as discussed in nasa/fpp#409. The changes bring the code more into line with approved C++ standards, by eliminating reliance on implicit conversions. I've made the required changes for the F Prime unit tests in this PR.

[LeStarch]

Closing this PR as it has been subsumed by #2707