Update build process, fix filesystemdiff bug

[RamblingCookieMonster]

Long story short, a number of tests now fail due to some changes in Pester. This is a temporary workaround gating the Pester version that we use to 3.4.6.

• Build files in separate folder
• Rename build to Start-Build for clarity
• Use PSDepend to pull in dependencies. Why? New version of pester doesn't like certain tests, gating until these are fixed.
• Change default psake task to Test, and parameterize start-build.ps1 for task
• FileSystemDiff used a full path for the NewName. Changed to the new filename alone. Left existing Logic for verbose output use

[RamblingCookieMonster]

@martin9700 - note the slight tweak to FileSystemDiff - hit me up if you have any concerns. Long story short, just swapped out -NewName $SomeFullPath with -NewName $NewFileName. Left original logic in place so that verbose output still has the full path.

[martin9700]

@RamblingCookieMonster Was the $SaveDiffPath causing a problem? Anyway, the change is fine. Are the FileSystemDiff tests working ok or need me to tweak anything?