Build debug and release configurations on AppVeyor

[sharwell]

Generally the two builds overlap. The primary differences between them are:

• Only the Debug configuration is used for code coverage reporting to codecov.io
• Only the Release configuration is used for deploying artifacts to NuGet

[codecov[bot]]

Codecov Report

Merging #38 into master will not change coverage. The diff coverage is n/a.

@@          Coverage Diff           @@
##           master     #38   +/-   ##
======================================
  Coverage    71.6%   71.6%           
======================================
  Files          36      36           
  Lines        3476    3476           
  Branches      299     299           
======================================
  Hits         2489    2489           
  Misses        860     860           
  Partials      127     127

[JohanLarsson]

Why both?

[sharwell]

@JohanLarsson Code coverage for tests is more accurate when optimizations are not applied to the assemblies. However, we only want deployments for the optimized binaries. By building both, both scenarios are supported.