add make dist and install targets

bin-dist tars into pkg/${PKG}.tar.gz
src-dist tars into pkg/${PKG}-src.tar.gz
PKG is only expanded once
make install untars pkg/${PKG}.tar.gz into PREFIX
doc-dist is not handled yet.
add libdisasm support (untested)
Add libpotion.so target
Support libpotion.so DEBUGFLAGS, fix ifdef HAVE_LIBDISASM
add make TAGS target, add .opic .SUFFIXES
adjust .gitignore for .opic et al
syntax.g: potion_code_ => YY_NAME()
fib.pn: behave like parrot example
config.sh: support lib, probe for libdis. support clang
Improve make perf: no DEBUG and DATE shell calls

Faster REVISION, add DEFINES to config.h to be more consistent.
double make speed by moving unneeded shell calls away

to dist.mak for make install dist tarball
pass PREFIX to dist.mak, add .so to dist, share/potion/ only

Special rule for core/callcc.opic
remove unneeded PKG macro from main Makefile
Change LOADER_PATH, support native load extensions, fix load readline

. at the begin of the LOADER_PATH is a security risc, put it at the end.
Search in lib and PREFIX/lib/potion before.
Search only for native load extensions: .so/.dylib/.dll
Store extensions for exe, load (.dylib), dll (.bundle) and lib in config.h, also provide them
in config.sh.
Move lib/readline/readline.so to the searchable lib/readline.so, fix uninstalled interactive mode.
load .pnb before .pn without timestamp check (yet).
Add .i target for CC -E -c preprocessed files.
add -Wno-unused-value for clang (also apples cc)
fix make dist

use exts, add more docs, pass exts from Makefile to dist.mak
make clean more
.gitignore cleanup
MAKE revamp: sync new config.inc with core/config.h

The external makefiles dist.mak, and for the libs now can use config.inc, which is synched
with core/config.h. Changed target config to do the obvious, new phonies config.h.echo and config.inc.echo.
dist.mak: protect make dist on empty PREFIX and DLLEXT, revamp PHONY