docs(README): add declaration reference (#159)

* docs(README): add declaration reference

* refactor(docs): move reference to separate document

* docs: fix errors in reference and move to README

* docs: fix errors ín readme

* docs: add examples to sequence of and bit string

* style: run cargo fmt

* fix(per): unbalanced brackets

* doc: make sure reference examples pass doctest

* docs(README): add type alias declaration examples