Slash escaping in BCQL

[jan-niestadt]

How slash escaping works seems to have accidentally changed in the dev branch. On older BlackLab versions, this will find a single open bracket:

[word="\("]

On the dev branch, you need to use two slashes:

[word="\\("]

Presumably this is because both the BCQL parser and Lucene's regex parser interpret \ as an escape character and take the next character to be literal, both removing one escape character.

We should decide how this should work (the top one probably, seems more intuitive for users and used to work that way).

[jan-niestadt]

Fixed in c67789d