Add a lookahead for DELETE to avoid mistaking HTTP strings for SQL

[illright]

Description of the Change

Currently, the uppercase DELETE is a trigger to initiate coloring for embedded SQL. That comes into conflict with the HTTP request descriptions, where DELETE is one of the allowed methods.

So an API-describing string like:

"""
GET /endpoint
POST /endpoint
DELETE /endpoint
PATCH /endpoint
"""

starts getting wrong highlighting starting from the DELETE keyword.

This PR aims to cover this particular case of the occurence of DELETE in a string.

Benefits

API descriptions in Python strings will look more appealing, and provided that servers are frequently written in Python, this is a considerable use case.

Possible Drawbacks

Looks a little hacky.

[calebmeyer]

Thanks for your submission!

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[illright]

@calebmeyer Could you please take a look at the latest failing build? I don't think it's failing because of my changes

[darangi]

Thanks @illright for your contribution,

The failure isn't related to your change, this is a problem with Travis service.