Guard against panic caused by misusing Compiler

Close: #149

Add compat wrapper for yr_compiler_add_fd (1.x)

Close #122

Keep alive of cgo handle id pointer

change uint to standard unsigned int

Fix copy/paste error

Add note for pkg-config-less static builds

fix: also malloc user data pointer in memory iterator

Bump YARA version for tests

Add 3rd uintptr->HANDLE conversion wrapper, move wrappers to compat.[ch]

Update requirements (cgo, README) to YARA v4.2