Add storage to highlighted words

[nfurfaro]

This PR aims to add the storage keyword to the list of highlighted words.
I'm not familiar with the code in this repo, so not sure if I need to do more or how to test my changes.
closes #46

[eureka-cpu]

1. to test for your branch read this: https://code.visualstudio.com/api/working-with-extensions/publishing-extension#packaging-extensions

2. the context in which this works is only if you add a name after the storage keyword. Essentially just need to allow the keyword itself, but the current state is that it's being treated the same as a struct or enum which will have a name after the keyword

This works:

storage Name {
    field: ...,
}

This doesn't:

storage {
    field: ...,
}