#29 DPTXlator2ByteFloat: inaccurate precision

[snickermicker]

DPTXlator2ByteFloat cannot represent the maximum and minimum values for this type.
Root cause seems to be in private method: fromDPT(). The accuracy when calculating the value is Float but might need to be Double.
The following test cases test the erroneous calculation: 0x7FFF should result in 670760.96 but results in 670760.94 and 0xF800 should result in -671088.64 but results in -671088.6.

[Boris Malinowsky]

Fixed in dev for v2.2.