LLVM 8 and loading from multiple shared libraries

Bugfix release

Support for LLVM 7.0

Thanks to foerdi

Support for LLVM 5.0 amd 6.0

Thanks to foerdi once again

Add support for dynamic loading

- Single shared library only (e.g. libLLVM-X.Y.Z.so)
- Switch from (dynamic/static) linking to dynamic loading by
  setting the D version LLVM_Load.
- Use LLVM.load / LLVM.unload for manual control over which
  shared library to use
- Additionally set D version LLVM_Autoload to try to load a
  platform appropriate default shared library for LLVM
- As compile time introspection is used to generate function pointers
  dynamic loading has increased compilation time.

Add target information to README

Support for LLVM 4.0

Thanks to foerdi who did the annoying part

Bug fix release

Bug fix release

Also updates the fibonacci example to show how to
correctly use MCJIT.

Wrong code in README example