[llvm-c] Implement LLVMPrintValueToString

Original patch by Chris Wailes
[OCaml] Implement Llvm.string_of_llvalue
[llvm-c] Expose IRReader interface

Original patch by Chris Wailes
[OCaml] Impement Llvm_irreader, bindings to LLVM assembly parser
[llvm-c] Expose LLVMLoadLibraryPermanently

Original patch by Chris Wailes
[llvm-c] Add functions for initializing native AsmPrinter, AsmParser & Disassembler

Original patch by Chris Wailes