Import/Export with comments

[mnordahl]

• Amend the file parser to accept (and ignore) comments using //
• Amend the save and export functionality to add comments, e.g.:

For proper interpretations of each value, see #2

0101 0011    // LD (42 -> OP1)
0010 1010    // 42
0101 0100    // LD (13 -> OP2)
0000 1101    // 13
0001 0000    // ADD
0100 0101    // MOV (RES -> OUT)
0101 0110    // RES, OUT
1100 0000    // PRD
1110 0000    // HLT