Support fine-grained search syntax

[thesephist]

Currently, a search query will match any part of a contact's card. It would be nice to be able to search a specific property, for example, search for "Berkeley" in the "Location" field only, so people who are associated with Berkeley the university will get filtered out. I propose the syntax attribute:keyword as a special syntax that is processed separately from the rest of the query. For example:

location:berkeley '24

Will find the intersection of the current results for '24 and the contacts with "berkeley" in the location field.

This can also apply multiple times. For example:

location:berkeley work:apple

finds everyone in the list who works at Apple, who lives in Berkeley.

The special field indicator all: matches all fields. This is nice for disambiguation. For example, if we want to search for the string 'work:apple' as a literal match rather than searching the "work" field, for example, we can type

all:work:apple

Which will match work:apple on all fields.

[thesephist]

My requirements on this have changed a bit, so I've implemented just the version of this that I will need to use Mira.

• Search scoped to one field field: value1 value2 value3

We do not support the all: syntax as colons generally don't appear in searched text. We also don't support multiple scoped keywords (intersection searches) as I don't think I need it. But if we do, we'll add it.