Use correct integer kind for zero enum initializer

Fixes regression exhibited (but not introduced) by previous commit.
Fix compilation for rarely-used extensions

LLVM and blocking graph extensions had old compilation
errors, undetected because they are not built by default.
API documentation for computed goto
Preserve cases in switch block with attribute

The problem went unnoticed because the list of cases is usually ignored,
except to build the CFG in --domakeCFG.

This closes #1812231.
Support range of values in case labels

Some programs use very large value ranges in switch statements:
  case 0 ... 0xffff:
Currently, CIL folds such ranges into a list of cases, but this may consume an
arbitrary amount of memory.

This patch:
- adds a constructor CaseRange to the Cil.label type;
- adds a --useCaseRange switch (disabled by default for backward compatibility);
- adds a function Cil.caseRangeFold to expand CaseRanges into lists of Cases.
Support case ranges in prepareCFG
Add whitespace to fix ocamldoc output
Do not run test using a lot of memory

On machines with limited amount of RAM, the system starts swapping a lot when
running testrun/sizeof3, before failing because time-limit is exceeded.
Add a regtest make target to run regression tests
Allow symlinks to cilly (#120)
Remove unneeded files
Remove useless code in Util
Move test scripts from ocamlutil to test
Remove deprecated references to perfcount
Move test-bad and teetwo from bin/ to test/
Remove .bat windows script
Move every perl script in lib/
Remove obsolete lib/Makefile
Add VERSION to Cilly.pm
First attempt of Makefile.PL