To get more compatibility with the go command, implement a similar
command line interface (with "tinygo build <package>" etc.).
Other than that, an all-round cleanup of command parsing.
This has the benefit of not requiring a 'runtime' IR file, so that
complete relocatable files can be built without requiring input IR.
This makes the compiler a lot easier to use without the Makefile.
Code size is not affected.
This reverts commit d9ca5f97fb.
There is a problem with coroutines that I haven't solved yet. Reverting
makes it work, for now.
Also, use a better coroutines flag for the LLVM opt tool.
