Features and improvements (#9) (#10)

* Removed `Queries` struct in favor of functions for individual queries.
* Support transactions for `sync` and `async`
* Batch query function params uses anything that implements `IntoIterator` rather than `Vec`
* Each future in the stream returned by `:batchmany` query returns stream from an iterator over rows instead of a stream from `Vec`
* `:many` query returns an Iterator over rows instead of a `Vec`
* Generic client implentation for `sync` and `async` clients
* Export `sqlc-derive` proc-macros from `sqlc-core` lib
* Code refactor
* Updated examples (with transactions)

Merge pull request #8 from easeq/batch-result-type-with-generics

Batch result type with generics

Merge pull request #7 from easeq/for-enum

Enum related issues and improvements

Merge pull request #6 from easeq/serde-support-examples

updated examples

Merge pull request #4 from easeq/fix-commit-error

Fix commit error

Merge pull request #2 from easeq/update

Add support for tokio-postgres, deadpool and complex types

Merge pull request #1 from easeq/clean-and-validate-gen-code

Cleanup and validate generated code