update docs to include separate responsive css, update docs to highlight proper file name, updated makefile to build responsive separately

lib/bootstrap.less

@@ -57,6 +57,3 @@
 
 // Utility classes
 @import "utilities.less"; // Has to be last to override when necessary
-
-// Responsive
-@import "responsive.less";

lib/responsive.less

@@ -3,6 +3,14 @@
 // -------------------------------------------------------------
 
 
+// REPEAT VARIABLES & MIXINS
+// -------------------------
+// Required since we compile the responsive stuff separately
+
+@import "variables.less"; // Modify this for custom colors, font-sizes, etc
+@import "mixins.less";
+
+
 // RESPONSIVE CLASSES
 // ------------------