Add Build Customizations option

Support Build Customization settings for projects. Now Premake5 can
recognize Build Customizations File that 3rd party API (e.g. CUDA)
maded.

src/_premake_init.lua

@@ -77,6 +77,12 @@
 		pathVars = true,
 	}
 
+	api.register {
+		name = "buildcustomizations",
+		scope = "project",
+		kind = "list:string",
+	}
+
 	api.register {
 		name = "builddependencies",
 		scope = { "rule" },

src/actions/vstudio/vs2010_vcxproj.lua

@@ -1313,6 +1313,7 @@
 	m.elements.importExtensionTargets = function(prj)
 		return {
 			m.importRuleTargets,
+			m.importBuildCustomizationsTargets
 		}
 	end
 
@@ -1330,6 +1331,12 @@
 		end
 	end
 
+	function m.importBuildCustomizationsTargets(prj)
+		for i, build in ipairs(prj.buildcustomizations) do
+	      premake.w('<Import Project="$(VCTargetsPath)\\BuildCustomizations\\%s.targets" />', path.translate(build))
+	   end
+	end
+
 
 
 	function m.importDefaultProps(prj)
@@ -1345,6 +1352,7 @@
 	m.elements.importExtensionSettings = function(prj)
 		return {
 			m.importRuleSettings,
+			m.importBuildCustomizationsProps
 		}
 	end
 
@@ -1362,6 +1370,12 @@
 		end
 	end
 
+	function m.importBuildCustomizationsProps(prj)
+		for i, build in ipairs(prj.buildcustomizations) do
+	      premake.w('<Import Project="$(VCTargetsPath)\\BuildCustomizations\\%s.props" />', path.translate(build))
+	   end
+	end
+
 
 
 	function m.importLibrary(cfg)