Feature Request: add support for ltree data type

[landure]

Please add support for PostgreSQL ltree extension, with

• ltree data type, mapping to a string.
• gist_ltree_ops indexes, created with a query like CREATE INDEX path_gist_idx ON test USING GIST (path gist_ltree_ops(siglen=100)); where 100 is a multiple of 4 signature length.
• @>, <@, @, ~, ? operators.

Ltree is a nice extension for tree structures.

[martin-georgiev]

@landure I think you will be happy to learn that all ltree functions are now also supported via #440

[landure]

Thank you for accepting my contribution :D

[martin-georgiev]

Thank you for doing it. It's much appreciated 😊