v0.5.0

Update iteration protocol (#70)

* replaced FPATH/WPATH to BASE_URL in tests

* rebased on number instead of index for extended_row

* rebased on simplified iteration protocol

* removed Iterator

* removed processors

* moved Error to exceptions.TabulatorException

* added extended row test

* parsers.api docstring fix

* made headers and row list instead of tuple

* added post_parse middleware hook

* updated examples

* added middlewares

* added middlewares test

* fixed table iterator

* fixed linting

* renamed middlewares to processors

* fixed tests

* added _rows prefix to processors

* added LoadingError and ParsingError

* added extract_headers to BC

* updated deprecations

* refactored topen signature

* implemented Table.sample

* added html detection

* fixed stream source example

* fixed linting error

* removed old comment from open

* updated readme

* updated readme

* Table.sample -> row[] instread of extended_row[]

* updated comment

* updated comment

* simplified code

* updated readme