Improve process helper

[asbjornu]

Checklist

• I have included examples or tests
• I have updated the change log
• I am listed in the CONTRIBUTORS file
• I have cleaned up the commit history (use rebase and squash)

Changes proposed in this pull request:

This PR wraps the setting of Process.PriorityClass in a try/catch so everything doesn't blow when trying to set it leads to System.ComponentModel.Win32Exception : Success (as @cvpcs is having problems with in GitTools/GitVersion#1070) or System.InvalidOperationException : Cannot process request because the process (2989) has exited (as @mkoertgen is having problems with in GitTools/GitVersion#720).

I think not being able to set the process' priority class does not warrant blowing up. I think not being able to set it (only failing on Mono/Mac it seems) will only lead to the process running at normal priority, which should be fine.

PS: Unfortunately, this PR also changes the EOL in some files, making it appear a much larger change than it actually is. The files had inconsistent line endings in the blob, making it very hard to work with on my Mac.

PPS: I'm not aware of any CONTRIBUTORS file or change log for this repository, which is why I haven't checked those two boxes above.

[GeertvanHorrik]

Too bad GitHub can't ignore non-relevant changes, but this looks good.

[asbjornu]

@GeertvanHorrik: Excellent, thanks! Now we just have to figure out how to get a new version of GitTools.Core published to NuGet. 🤔

[pascalberger]

@asbjornu @GeertvanHorrik Where are we regarding publishing a new version of the core package? I think it's really important to push this forward so that we can fix the build pipeline in GitVersion and can move on to accept PRs again

[gep13]

@pascalberger as per the discussion on Gitter, I think we are waiting to arrange a Skype call with @JakeGinnivan to walk through the current process, and to get it fully documented. If you can help in getting something arranged to facilitate that, I think it would be great!

[JakeGinnivan]

I put a PR up which explains the process on BitBucket. I have also done a release and am getting the builds green again :)

[gep13]

@JakeGinnivan sweet!

[asbjornu]

@JakeGinnivan: Fan-tas-tic! 😄 👍