Move generated files to gen subdir. This allows to:
1. Rebuild init.go without rebuilding generated code.
2. Excluding generated files from gometalinter checking.
This makes faster and consume less memory.
Update #538
1. mmap all memory always, without explicit mmap calls in the program.
This makes lots of things much easier and removes lots of code.
Makes mmap not a special syscall and allows to fuzz without mmap enabled.
2. Change address assignment algorithm.
Current algorithm allocates unmapped addresses too frequently
and allows collisions between arguments of a single syscall.
The new algorithm analyzes actual allocations in the program
and places new arguments at unused locations.
This is mostly copied form linux.
We probably need better support for sharing descriptions
between multiple OSes. But there are lots of differences,
so this is not trivial.
