update TODO list
Merge pull request #22 from regehr/todo

update TODO list
Merge remote-tracking branch 'upstream/master' into undefined
Fixed the mulNW and shlNW instruction, removed tab characters as per review comments

This patch fixed:
1. MulNW and ShlNW instruction - Build mul/shl expr and then added assertions for UB.
2. Removed all tab characters by spaces.
3. Merged the computation of any expression and return statement into one return
statement itself. For eg. in addnuw and many more like this.

TODO: to fix sdiv yet !!