Improves parsing speed

[joreg]

Especially with the faster A2 sensor scanning is very slow and getting slower over time. Turned out the serialPort incoming buffer was increasing steadily because bytes were not read fast enough.

This PR does the following two things:

• Instead of reading bytes one-by-one from the serialPort, it always reads the whole available buffer in one operation
• Reusing a global responseBuffer instead of allocating a new one for each response

This most likely will solve #2