FIX: address issue where PROJ core dumps on proj_create with +init= when global context does not have data directory set

[snowman2]

• Closes 2.3.0 seg faults under Ubuntu #415
• Closes PROJ 6.1+ (pyproj 2.2+ wheels) incompatible with previous versions #368 (I hope)
• Fully documented, including history.rst for all changes and api/*.rst for new API

[snowman2]

Before:

>>> from pyproj import CRS
>>> cc = CRS("+proj=utm +zone=33 +ellps=WGS84 +datum=WGS84 +units=m +no_defs")
>>> cc = CRS(init="epsg:4326")
Segmentation fault (core dumped)

After:

>>> from pyproj import CRS
>>> cc = CRS(init="epsg:3857")
>>> cc
<Projected CRS: EPSG:3857>
Name: WGS 84 / Pseudo-Mercator
Axis Info [cartesian]:
- E[east]: Easting (metre)
- N[north]: Northing (metre)
Area of Use:
- name: World - 85°S to 85°N
- bounds: (-180.0, -85.06, 180.0, 85.06)
Coordinate Operation:
- name: Popular Visualisation Pseudo-Mercator
- method: Popular Visualisation Pseudo Mercator
Datum: World Geodetic System 1984
- Ellipsoid: WGS 84
- Prime Meridian: Greenwich

[jorisvandenbossche]

Small remark here: it might be useful to add a comment on why this line is here (maybe linking to one of the issue explaining it).

I was actually reading this code in one of the other PRs and already wondering why the search paths were set twice.

[snowman2]

That's a good idea. I would like to change this solution in 2.4 as I don't want to reset the global context each time. It's okay in this context as it is only set once.