Allow TextClause in Index __init__

[isra17]

Quick fix that allow support for:

# From official doc
from sqlalchemy import text

Table("sometable", metadata,
                Column("name", String(50)),
                Column("address", String(100)),
                Index("some_index", text("lower(name)"))
        )

[ilevkivskyi]

Thanks! I have just one question.

Could you please also add a test case for this (e.g. the one you mention in the PR description)? The test cases live in test/test-data in .test files.

[isra17]

Could you please also add a test case for this (e.g. the one you mention in the PR description)? The test cases live in test/test-data in .test files.

Done

[ilevkivskyi]

👍