MINOR: Add a proper Makefile to build project.

Inspired from mod_virtualvalue

Also, don't make reference to any version in code or elsewhere, this now
come from git describe and CFLAGS definition

Build the project (one of) :
 $ make
 $ make shared
 $ make all
  CC     mod_ruid2.o
  CC     mod_ruid2.so

Build with verbose output :
 $ make V=1
cc -c -DMODULE_NAME='"mod_ruid2"' -DMODULE_VERSION='"v0.9.8-6-g20ec6cc-dev"' -fPIC -I/usr/include/apache2 -D_REENTRANT -D_GNU_SOURCE -pthread -I/usr/include/apr-1   -W -Wall -o mod_ruid2.o mod_ruid2.c
ld -shared -o mod_ruid2.so mod_ruid2.o  -lapr-1 -luuid -lrt -lcrypt -lpthread -ldl  -lcap

Build with specific CFLAGS and CC :
 $ make CC=i586-pc-linux-gnu-gcc CFLAGS='-march=geode -Os -mmmx -m3dnow -I/data/cross/alix3-i586/firmware/usr/include'

In this case default one (-fPIC is alway applied).

Strip library :
 $ make strip
  STRIP  mod_ruid2.so

Build a tar for public release :
 $ make dist
  TAR    mod_ruid2-v0.9.8-6-g20ec6cc-dev.tar
  XZ     mod_ruid2-v0.9.8-6-g20ec6cc-dev.txz
BUG/MEDIUM: make RGroups working in mode stat, not only config mode

Also copy the Rgroups from parent to child when merging configurations.

That kind of configuration was broken :

  <VirtualHost *:80>
    DocumentRoot /var/www/localhost/htdocs

    RMode stat
    Rgroups nogroup
    RMinUidGid     #1000  #1000
    RDefaultUidGid apache apache
  </VirtualHost>