included missing lemmas
partial progress on proving list head example
checked truth value before pattern expansion
refactoring: adding helper methods to simplify common operations
updated head.spec and included it in regression test
revised head_spec
Merge pull request #830 from yilongli/prove-simple-list-head

Prove simple list head
proved kernelc list head example
proved kernelc list tail
proved list add example
list swap example requires the prover to be able to unroll the list pattern more than once in a single step
proved kernel c list swap example