update readme feature table

Author: micahrj

README.md

@@ -14,12 +14,9 @@ Below is a proposed list of milestones (roughly in-order) and their status. Subj
 | ----------------------------------------------- | ------------------ | ------------------ | ------------------ |
 | Spawns a window, no parent                      | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
 | Cross-platform API for window spawning          | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
-| Window uses an OpenGL surface                   | :heavy_check_mark: |                    | :heavy_check_mark: |
 | Can find DPI scale factor                       |                    | :heavy_check_mark: | :heavy_check_mark: |
 | Basic event handling (mouse, keyboard)          | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
 | Parent window support                           | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: |
-| Send messages                                   |                    | :heavy_check_mark: |                    |
-| *(Converge on a common API for all platforms?)* |                    |                    |                    |
 
 ## Prerequisites