Update mjolnir dependency

Now a personal fork (includes a critical bugfix)
Add `gen-const` to generate different constants

Also includes a string generator that's actually awful and will explode
performance (at the moment)
Add host invocation and a sample runtime library
Replace mjolnir with homebrew system
Fix verification
Enable more optimization passes
Enable verification and optimization in compilation
Remove unused `:ref` field in `*current-fn*`
Add `analyze-forms` function
Refactor compilation functions

It is now possible to disable LLVM optimizations and IR dumping
Add `compile-forms` method
Add a few specs

Integration tests, not isolation tests
(can someone tell me how to unit test a compiler plz)
Add verbosity option
Use slingshot for exceptions
Separate `clj-llvm.compiler` into two namespaces

`gen-` functions are now `build-` functions, and live in
`clj-llvm.builder`; the actual compilation functions still exist in
`clj-llvm.compiler`
Remove unused members from `kw->cast-fn`
Make `runtime` a bit easier to read
Add proper `do` support

An explicit `ret` op is now required in a block, and creating a block
is now done with `llvm/block` instead of `llvm/do-`. Additionally, a
secondary `llvm/doall` function has been added, which is used to build
regular (non-function-body) `do` statements.