Pymapd

This release updates the support for higher-precision timestamps in pymapd.

https://github.com/omnisci/pymapd/pull/171

Issue with Windows and Python 3.7 around shared memory. Fix was to disable checking of shared memory functions on Windows, as shared memory via `select_ipc` and `select_ipc_gpu` not supported (shared memory functionality requires Python code to be running on same machine as OmniSci installation; OmniSci does not currently install natively on Windows, so shared memory functionality not currently possible)

pymapd `__version__` dunder erroneously removed in v0.8; this release adds the variable back.

This release of pymapd is the first Python 3 only release (3.5 - 3.7 supported); users needing Python 2 support should use pymapd 0.7.1 but plan to upgrade as soon as possible, as no further maintenance will be provided to support Python 2.

With OmniSci 4.5, we changed the default installation ports for connecting to the core database, and this change is reflected in this release. Depending on your OmniSci implementation, you might still be using 9091 or 6274 for the binary connection. If you are having trouble connecting using pymapd, verify port and specify it explicitly using `port=6274` in the connection string.

__Notable PRs:__
Drop support for Python 2 (155)
Update for pyarrow 0.12 (157)
Add Date in days conversion support (168)
Switch references from 9091 to 6274 (173)

Fixed typo with columnar load datetime conversion (153)

This release is the first pymapd release switching over to the cudf library for GPU dataframes (prior releases of pymapd supported pygdf, the prior version to cudf). Also supported are pyarrow 0.11.0 for `select_ipc` as well as Python 3.7.

Note that if you install cudf, cudf requires pyarrow 0.10.0 and pymapd will downgrade pyarrow to allow installation.

Finally, the need for Cython to compile pymapd has been removed, which should hopefully fix any outstanding issues when installing from pip.

__Notable changes__:
Fix bug with loading Pandas dataframe row-wise (133)
Allow ints and string inputs for TIMESTAMP columns (138)
ENH: migrate to cudf (139)
Update IPC code to remove Cython (148)
Add support for pyarrow 0.11 and python3.7, remove python 3.4 (151)