Utilities for adding indexes

[simonw]

Both in the Python API and the CLI tool. For the CLI tool this should work:

$ sqlite-utils create-index mydb.db mytable col1 col2

This will create a compound index across col1 and col2. The name of the index will be automatically chosen unless you use the --name=... option.

Support a --unique option too.

[simonw]

https://www.sqlite.org/lang_createindex.html

May as well support --if-not-exists as well.

[simonw]

The WHERE clause can be used to create partial indexes: https://www.sqlite.org/partialindex.html

I'm going to ignore it for the moment.

[simonw]

Likewise I'm going to ignore indexes on expressions (as opposed to just columns): https://www.sqlite.org/expridx.html