features: Support more than 32 features!

Currently features are represented as bits in a 32bit mask so we
obviously can't have more than 32 features with that approach. The new
approach is to use the COGL_FLAGS_ macros which lets us handle bitmasks
without a size limit and we change the public api to accept individual
feature enums instead of a mask. This way there is no limit on the
number of features we can add to Cogl.

Instead of using cogl_features_available() there is a new
cogl_has_feature() function and for checking multiple features there is
cogl_has_features() which takes a zero terminated vararg list of
features.

In addition to being able to check for individual features this also
adds a way to query all the features currently available via
cogl_foreach_feature() which will call a callback for each feature.

Since the new functions take an explicit context pointer there is also
no longer any ambiguity over when users can first start to query
features.

Reviewed-by: Neil Roberts <neil@linux.intel.com>

cogl/cogl-buffer.c

@@ -134,10 +134,10 @@ bo_map (CoglBuffer       *buffer,
   _COGL_GET_CONTEXT (ctx, NULL);
 
   if ((access & COGL_BUFFER_ACCESS_READ) &&
-      !cogl_features_available (COGL_FEATURE_MAP_BUFFER_FOR_READ))
+      !cogl_has_feature (ctx, COGL_FEATURE_ID_MAP_BUFFER_FOR_READ))
     return NULL;
   if ((access & COGL_BUFFER_ACCESS_WRITE) &&
-      !cogl_features_available (COGL_FEATURE_MAP_BUFFER_FOR_WRITE))
+      !cogl_has_feature (ctx, COGL_FEATURE_ID_MAP_BUFFER_FOR_WRITE))
     return NULL;
 
   target = buffer->last_target;