Support UPPER & LOWER non-aggregating functions

Remove StoreError, now fetch_schema returns Result<Option<Schema>>.
StoreError::SchemaNotFound was error, but now it simply returns "None".

Change Store->fetch_schema interface return type to Option<_>,

[Revised] Support Plus(+) and Minus(-) signs in WHERE

Convert generate_id, insert_data and delete_data to async.
Now all StoreMut functions provide async

Getting familiar with using TryStreamExt

…rror

…N test cases!

Replace or-iterator to or-stream.
Update BlendContext retun type to Option rather than Result.

FilterContext can have both content & children or only children.

Convert store traits to async

Resolves: #111

Resolves: #109, #110

Resolves: #112

Resolves: #113
Resolves: #46
Resolves: #105

bulky & needless

* Flexible

* Update & Delete

(Clippy messed up fmt)

* Update Umya

* Delete optimisation

* Revert "Delete optimisation"

This reverts commit 1b2ff42.

* Init sheets

* Lazy doesn't work very well yet

* Remove local dev ref

* Use git for temp crate

* fmt, Save changes

* Clean up execution

* issue

* `cargo fix`

* `cargo clippy --fix`

* `cargo fmt`

* fail fast

* fix

* fmt

* Remove iter box

* Fix

* `cargo fix`

* `cargo fmt`

* Store

* StoreMut

* fmt

* Lots of improvement
(done yesterday, didn't commit)

* Fix from update

* `cargo fix` & `cargo fmt`

* Get rid of memory tests for now

* New

* Done, just need to implement

* Rudamentary impl

* Rename table for sled

* fix

* `cargo fix` & `cargo fmt`

* Nearly ready

* IndexAdd doesn't need action

* fmt

* ColumnAdd

* Sled ColumnRemove

* Fixes & Sled IndexRemove

* Done!

* fmt

* Clip

0.2.0
Update Umya