Use Config class to write config during init_project.

[bdice]

Description

This uses the Config class (not to be confused with the new immutable _ProjectConfig class or the ConfigObj class from which it inherits) to initialize projects.

Potential breaking behavior: The signac.rc files generated after this change will differ from the previous configuration files by whitespace (spaces around the equals signs). The configs are parsed the same as before.

Motivation and Context

The previous code didn't work if the project name contained commas. Resolves #251.

Types of Changes

• Documentation update
• Bug fix
• New feature
• Breaking change^{1
  1}The change breaks (or has the potential to break) existing functionality.

Checklist:

• I am familiar with the Contributing Guidelines.
• I agree with the terms of the Contributor Agreement.
• My name is on the list of contributors.
• My code follows the code style guideline of this project.
• The changes introduced by this pull request are covered by existing or newly introduced tests.

If necessary:

• I have updated the API documentation as part of the package doc-strings.
• I have created a separate pull request to update the framework documentation on signac-docs and linked it here.
• I have updated the changelog.

[codecov]

Codecov Report

Merging #252 into master will increase coverage by 0.09%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #252      +/-   ##
==========================================
+ Coverage   64.96%   65.06%   +0.09%     
==========================================
  Files          39       39              
  Lines        5580     5581       +1     
==========================================
+ Hits         3625     3631       +6     
+ Misses       1955     1950       -5

Impacted Files	Coverage Δ
signac/contrib/project.py	90.97% <100%> (+0.01%)	⬆️
signac/common/config.py	70.37% <0%> (+4.62%)	⬆️

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[vyasr]

I'm willing to accept the possibility that people who are manually reading the signac.rc file and parsing it might have to deal with slightly different whitespace. I don't think that's a meaningful change as long as all of our existing functions (both Python and CLI) will work. As long as existing configs get parsed correctly either way (and therefore users can still manually create signac.rc files using a text editor), I don't think it's a problem.