Accept Python 3.6 path-like objects for read_env

[sergeyklay]

References:

• Support path-like objects #106
• Can't use WindowPath in read_env() method #286
• Accept python 3.6 path-like objects for read_env #107
• Allows use of Path objects when reading env from the filesystem. #281
• Add clean fix for WindowsPath type when calling read_env() method #287

[coveralls]

Coverage increased (+0.1%) to 89.569% when pulling 1a6b758 on feature/pathlike into 68d9544 on develop.