`cutil.from_dc_charpointer()` is guaranteed to return `str`, while
`cutil.from_optional_dc_charpointer()` may return `None` if C function
returns `NULL`.
`deltachat.const` module now defines `__getattr__` and `__dir__` as
suggested by https://www.python.org/dev/peps/pep-0562/
mypy detects that `__getattr__` is defined and does not show errors
for `DC_*` constants which cannot be detected statically.
mypy is added to `tox.ini`, so type check can be run with `tox -e mypy`.
utcfromtimestamp() is not recommended by the official documentation,
because many methods, including timestamp(), work incorrectly with
"naive" datetimes returned by utcfromtimestamp().
* import python, try to adapt for rust
* add missing wrapper functions
* - try to write up how to build python bindings
- strike some unused functions from deltachat.h
* adjustments to make tox work
* try to run circle-ci with python build
* don't do docs
* running cargo test as well
* don't run cargo test anymore, that's done in other ci jobs
* also build docs
* don't run doxygen anymore
* subst C with Rust
* a try to get better wheels
Closes#41
