Format specifiers in f-strings don't highlight the entire thing in a consistent manner

Nadie ha tomado este issue todavía.

Hello. Sometimes the `:...` aspect of a format string is highlighted in its entirety but often times it's not. I would like to know if it's possible to make it so it's all under the same consistent scope or if it's by design that it doesn't. My main use case has to do with types using a custom `__format__`.

For example:


I would have imagined both of these to fall under the same scope but they're not.

The first screenshot goes `source.python` > `meta.fstring.python` > `storage.type.format.python`
The second screenshot goes `source.python` > `meta.function-call.python` > `meta.function-call.arguments.python` > `meta.fstring.python`

A regular line of code without using custom `__format__` (e.g. `{test:.2f}`) goes as `source.python` > `meta.function-call.python` > `meta.function-call.arguments.python` > `meta.fstring.python` > `storage.type.format.python` which is what I would expect the other two to return as well, unless it's meant to be treated differently.

* **Editor name and version**: Sublime Text 3.2.1 Build 3207
* **Platform**: Windows 8.1
* **Color scheme**: Custom
* **MagicPython version**: 1.1.1
* **A sreenshot**: See above
* **5-10 lines of surrounding code**: In the screenshot hopefully

Empieza reproduciendo los dos ejemplos de f-string en Sublime Text 3.2.1 con MagicPython 1.1.1 e inspecciona sus ámbitos de sintaxis, comparándolos con el ejemplo regular `{test:.2f}`. Se considera terminado cuando los especificadores de formato de los casos reportados reciben un ámbito coherente, o cuando el comportamiento se documenta como intencionado.

Escrito por el modelo de indexación a partir del texto del issue.