release-1.4

This release makes some minor improvements to the handling of FOR-NEXT loops:

• The increment of a loop can now be fractional as per #63:
  • FOR I=1 TO 2 STEP 0.1
• The termination condition uses a little rounding to mask float-based drifting.

As a result of fuzz-testing we've also improved the parsing of FN, NEXT, and STEP tokens (#65, #66, #67).

Finally the PRINT statement will accept ; as being synonymous with ,, which eases porting programs written for BBC BASIC.