1) Added functionality to default install to "c:\program files (x86)\Common Files\Modules" if not $Destination is provided
2) All module destination paths will get added to either the User or Machine (if -Global  switch is true) $env:PSModulePath environment variable
Fixed 2 failing tests
"Should output objects from Get-PsGetModuleInfo that have properties matching parameters of Install-Module"
"Should support piping from Get-PsGetModuleInfo to Install-Module"

The ModuleUrl returned from the Get-PsModuleInfo function was set to the ProjectUrl, which was not valid when attempting to download with Install-Module
More work to support correct use of environment variables

 * Added new Pester test file (PsGet.tests.ps1)
 * Added test initiator file (Run-Tests.ps1)
 * Added global variables in PsGet.psm1 to store the default User and Global module paths
 * Added "PersistEnvironment" switch that when present will permanently update the User or Machine (if -Global specified) PSModulePath environment variable
 * Moved the setting of the $Destination variable to the beginning of the Install-Module function (This just alleviated some complexity)
 * Updated the CheckIfNeedInstallAndImportIfNot function to handle the case where a module is installed in multiple locations
 * Updated the CheckIfNeedInstallAndImportIfNot function to handle the case where the new install location differs from an existing install location (if they differ, then assume it is not installed)
 * Added new PsGet exported module function "Remove-PathFromEnvironmentVariable", really just used in testing to keep the PSModulePath environment variable from getting polluted
 * Update "Add-PathToEnvironmentVariable" function to take the -PersistEnvironment switch that when specified, will persist the change to either User or Machine environment
Deleted original tests because they have been moved in the PsGet.tests.ps1 file in the Pester testing framework format