Improvements for camera-ready

[AlviseDeFaveri]

This PR was initially meant to fix #2 but has grown to also improve state splitting logic in general.

Current content of the PR:

• EXPR hooks that adds annotations for CMOVE/SEXT expressions
• BranchAnalysis now only considers CMOVE constraints when analyzing CMOVE-dependencies (duh)
• New state restart from latest PC after splitting
• State is splitted also if an if-then-else statement is found in a branch condition (see test case) cmove_branches

Also fixed some issues in AST transformations for SEXT-like expressions and added a unit test for that.

Currently undergoing tests - do not merge.