mkxp.pro: Make MRI version a qmake config option

Example: qmake MRIVERSION=2.2

README.md

@@ -71,7 +71,7 @@ By default, mkxp switches into the directory where its binary is contained and t
 
 To auto detect the encoding of the game title in `Game.ini` and auto convert it to UTF-8, build with `CONFIG+=INI_ENCODING`. Requires iconv implementation and libguess. If the encoding is wrongly detected, you can set the "titleLanguage" hint in mkxp.conf.
 
-**MRI-Binding**: pkg-config will look for `ruby-2.1.pc`, but you can modify mkxp.pro to use 2.0 instead. This is the default binding, so no arguments to qmake needed (`BINDING=MRI` to be explicit).
+**MRI-Binding**: pkg-config will look for `ruby-2.1.pc`, but you can override the version with `MRIVERSION=2.2` ('2.2' being an example). This is the default binding, so no arguments to qmake needed (`BINDING=MRI` to be explicit).
 
 **MRuby-Binding**: place the "mruby" folder into the project folder and build it first. Add `BINDING=MRUBY` to qmake's arguments.
 

mkxp.pro

@@ -267,7 +267,11 @@ BINDING_MRUBY {
 }
 
 BINDING_MRI {
-	PKGCONFIG += ruby-2.1
+	isEmpty(MRIVERSION) {
+		MRIVERSION = 2.1
+	}
+
+	PKGCONFIG += ruby-$$MRIVERSION
 	DEFINES += BINDING_MRI
 
 #	EMBED2 = binding-mri/module_rpg.rb