Bug array of one

[dmweir]

Allow arrays of length one for most date types. If the field was created using array syntax in the message def, use an index to access the single element in the array, i.e msg.arr[0] not msg.arr.

Exceptions:
Fields that use a char array of length one will resolve as a scalar i.e. char[1] will become char. We only allow char arrays of size greater than one to ensure that there is spot for a null terminator byte. This logic is validated in the String validator type.

• Auto padding with now use the byte type and will internally always be ByteArray instead of a mix Char and String
• Accessing individual elements of ByteArray field will return an int, a slice will return a python bytearray.
• Unit tests for setting and getting fields that are arrays of length one have been added.