Min gw fix and windows installer batch file updated

Changes MinGW to use the Windows OS runtime by default. If not MinGW, it retains the included runtime as default.

Installer now checks for a list of library names to link against. Some bugfixes included also.
Installer now writes the `variables` section in the config file with the runtime and library link file mentioned
Installer now also checks for conflicting options and provides user feedback (/L with some others)
Installer now generates more verbose output so the user can actually check what and why stuff was installed.

example output:
````
LuaRocks 2.0.x installer.

Looking for Lua interpreter
   checking c:\users\public\lua\5.1
      Found .\\bin\\lua.exe
Interpreter found, now looking for link libraries...
   checking for c:\users\public\lua\5.1\\lua5.1.lib
   checking for c:\users\public\lua\5.1\\lua51.dll
   checking for c:\users\public\lua\5.1\\liblua.dll.a
   checking for c:\users\public\lua\5.1\lib\\lua5.1.lib
   checking for c:\users\public\lua\5.1\lib\\lua51.dll
   checking for c:\users\public\lua\5.1\lib\\liblua.dll.a
   checking for c:\users\public\lua\5.1\bin\\lua5.1.lib
   checking for c:\users\public\lua\5.1\bin\\lua51.dll
      Found lua51.dll
Link library found, now looking for headers...
   checking for c:\users\public\lua\5.1\\lua.h
   checking for c:\users\public\lua\5.1\include\\lua.h
      Found lua.h
Headers found, now testing interpreter...
  Ok

Will configure LuaRocks with the following paths:
LuaRocks       : c:\users\public\lua\LuaRocks\2.0
Lua interpreter: c:\users\public\lua\5.1\bin\\lua.exe
Lua binaries   : c:\users\public\lua\5.1\bin\
Lua libraries  : c:\users\public\lua\5.1\bin\
Lua includes   : c:\users\public\lua\5.1\include\
Binaries will be linked against: lua51.dll

Removing c:\users\public\lua\LuaRocks\2.0...
The system cannot find the path specified.

Installing LuaRocks in c:\users\public\lua\LuaRocks\2.0...
Created LuaRocks command: c:\users\public\lua\LuaRocks\2.0\luarocks.bat
Created LuaRocks command: c:\users\public\lua\LuaRocks\2.0\luarocks-admin.bat

Configuring LuaRocks...
Created LuaRocks site-config file: c:\users\public\lua\LuaRocks\2.0\lua\luarocks\site_config.lua
Created LuaRocks config file: c:\users\public\lua\LuaRocks\config.lua

Creating rocktrees...
Rocktree exists: "c:\users\public\lua\5.1"
Rocktree exists: "C:\Users\Thijs\AppData\Roaming\luarocks"

   *** LuaRocks is installed ***

You may want to add the following elements to your paths;
PATH     :   c:\users\public\lua\5.1\bin\;c:\users\public\lua\LuaRocks\2.0
LUA_PATH :   c:\users\public\lua\5.1\share\lua\5.1\?.lua;c:\users\public\lua\5.1\share\lua\5.1\?\init.lua
LUA_CPATH:   c:\users\public\lua\5.1\bin\\lua\5.1\?.dll

C:\Temp>
````