Add support for unstable Python versions (#38)

* Add support of unstable versions to package generation (#2)
* Add support of symver versions to Python setup scripts and tests

Co-authored-by: Maksim Petrov <47208721+vmapetr@users.noreply.github.com>
Co-authored-by: MaksimZhukov <v-mazhuk@microsoft.com>
Co-authored-by: Maxim Lobanov <v-malob@microsoft.com>

builders/python-version.psm1

@@ -0,0 +1,45 @@
+function Convert-Label() {
+    <#
+    .SYNOPSIS
+    Convert generic semver label to native Python label.
+    #>
+
+    param(
+        [Parameter(Mandatory)]
+        [string] $label
+    )
+
+    switch ($label) {
+        "alpha" { return "a" }
+        "beta" { return "b" }
+        "rc" { return "rc" }
+        default { throw "Invalid version label '$label'" }
+    }
+}
+
+function Convert-Version {
+    <#
+    .SYNOPSIS
+    Convert generic semver version to native Python version.
+    #>
+
+    param(
+        [Parameter(Mandatory)]
+        [semver] $version,
+        [char] $delimiter = "."
+    )
+
+    $nativeVersion = "{0}.{1}.{2}" -f $version.Major, $version.Minor, $version.Patch
+
+    if ($version.PreReleaseLabel)
+    {
+        $preReleaseLabel = $version.PreReleaseLabel.Split($delimiter)
+        
+        $preReleaseLabelName = Convert-Label -Label $preReleaseLabel[0]
+        $preReleaseLabelVersion = $preReleaseLabel[1]
+
+        $nativeVersion += "${preReleaseLabelName}${preReleaseLabelVersion}"
+    }
+
+    return $nativeVersion
+}