v1.0 rewrite

[jwodder]

Closes #8.

To do:

• Remove move_first
• Remove delay_open and open()
• When the input path points to a symlink and backup_ext is given, append the backup extension to the resolved path rather than to the pre-resolved path.
• Remove readall()
• Drop support for Python 3.7
• Remove InPlaceText and InPlaceBytes
• Split InPlace into text-only InPlace and bytes-only InPlaceBytes (no mode argument)
• Add type annotations (Closes Mypy type compliance #6)
• Give InPlace binary read1() and readinto1() methods
• Clean up/improve tests

[codecov]

Codecov Report

Merging #9 (5c47411) into master (da88595) will increase coverage by 1.96%.
The diff coverage is 94.96%.

@@            Coverage Diff             @@
##           master       #9      +/-   ##
==========================================
+ Coverage   93.00%   94.96%   +1.96%     
==========================================
  Files           1        1              
  Lines         200      159      -41     
  Branches       39       18      -21     
==========================================
- Hits          186      151      -35     
+ Misses          9        8       -1     
+ Partials        5        0       -5     

Files	Coverage Δ
src/in_place/__init__.py	94.96% <94.96%> (ø)