Tgcf

- Make the plugin architecture robust. (old way of writing plugins will break) Developers can write plugins with more ease. Plugins can modify files now, besides text.
- Add new plugins for watermarking and ocr.

merges prs 135 133

fix 122

merge pr 121 that fixes 15 and 120

merge pr 117 that fixes 104 and fixes 84

fix 72 and 73