- Fixes #56

Signed-off-by: Dan Ryan <dan.ryan@canonical.com>

- Add `wheel_cache` context manager helper for managing global context
  when creating wheel wheel_cache instances
- Add optional `check_supports_wheel` argument to `Resolver.resolve()`
  call when expected arguments include this one
- Inspect `InstallRequirement.ensure_build_location()` method and
  include `autodelete` kwarg if it is expected
- Update argument types passed into `resolver.resolve` which, as of
  `pip>=20.1` will expect a list of `InstallRequirement` instances
- Update `Resolver` import path to point at new location
  (`resolution.legacy.resolver`)
- Add necessary `global_tempdir_manager` contexts in tests
- Fix expected `RequirementSet.cleanup()` call after
  `Resolver.resolve()` which no longer applies due to use of transient
  `RequirementSet`
- Fixes #58
- Fixes #59
- Fixes #60
- Fixes #61
- Fixes #62

Signed-off-by: Dan Ryan <dan.ryan@canonical.com>

Signed-off-by: Dan Ryan <dan.ryan@canonical.com>

Fix appveyor pip version installed on python3.4

Signed-off-by: Dan Ryan <dan.ryan@canonical.com>

Remove python 3.4 from appveyor config

Signed-off-by: Dan Ryan <dan.ryan@canonical.com>

Dont install readme-renderer on python 3.8

- Readme-renderer depends on cffi due to lack of wheels built for
  cmarkgfm
- Build seems to fail for python 3.8 on appveyor

Signed-off-by: Dan Ryan <dan.ryan@canonical.com>

Install wheel and setuptools

Signed-off-by: Dan Ryan <dan.ryan@canonical.com>