Bug: Upper case expressions not supported

[wnienhaus]

Current behaviour:

Expressions with hex characters in uppercase cause assembly to fail with the error ValueError: Unsupported expression.

Expected behaviour:

The expected behaviour is that uppercase hex characters are treated identically to lower case hex characters.

Example:

This code fails to assemble with "Unsupported expression"

entry:
  move r0, 0x7FE - 1

While this code is successfully assembled without error:

entry:
  move r0, 0x7fe - 1

The only difference in the two code snippets is the hex value 0x7FE being upper case in one example (the failing one) and lower case in the other (the successful one).