Apiritif

- add external handlers feature

- support client-side certificates
- improve error trace info
- fix problem of binary POST tracing
- detect delimiter in csv files automatically

- add quoting auto detection feature
- add ability to log actions externally
- extend trace context

- improve csv encoding
- fix assertion trace for multi-asserts
- add 'assert_status_code_in' assertion
- migrate onto modern jsonpath_ng
- add lxml for cssselect
- add CSSSelect assertion

- fix cookies processing
- fix threads closing

- generalize handler interface