Backport environ and related code

[PiDelport]

This backports:

• environ
• environb
• get_exec_path
• getenv
• getenvb
• popen
• supports_bytes_environ

[codecov-io]

Current coverage is 87.98%

Merging #2 into master will decrease coverage by -9.04% as of a26a840

@@            master      #2   diff @@
======================================
  Files            5       6     +1
  Stmts          168     741   +573
  Branches        26      88    +62
  Methods          0       0       
======================================
+ Hit            163     652   +489
- Partial          2      16    +14
- Missed           3      73    +70

Review entire Coverage Diff as of a26a840

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