Reorganize tests

- Pester source code moved to `test/Pester`, deleted `ext-src`.
- Pester tests (.ps1 files) moved to `test/powershell`
- xUnit tests (.cs files) moved to `test/csharp`
- Third-party script test moved to `test/shebang`

test/powershell/assets/SortTest.txt

@@ -0,0 +1,5 @@
+5
+10
+3
+4
+8

test/powershell/assets/TestCsv.csv

@@ -0,0 +1,5 @@
+Column1,Column2,Column 3
+data1,1,A
+data2,2,B
+data3,3,C
+data4,4,D

test/powershell/assets/TestCsv2.csv

@@ -0,0 +1,3 @@
+Name,Planet,Heads,Arms,Brains,Assessment
+Zaphod BeebleBrox,Beetlgeuse,2,3,Indeterminant,Dangerous
+Arthur Dent,Earth,1,2,Some,Harmless (Mostly)

test/powershell/assets/TestJson.json

@@ -0,0 +1,14 @@
+{
+    "Name": "Zaphod Beeblebrox",
+    "Planet": "Betelgeuse",
+    "Appendages": {
+        "Heads": 2,
+        "Arms": 3
+    },
+    "Achievements": [
+        "Invented the Pan Galactic Gargle Blaster",
+        "Worst Dressed Sentient Being in the Known Universe",
+        "The best Bang since the Big One",
+        "One hoopy frood"
+    ]
+}

test/powershell/assets/testablescript.ps1

@@ -0,0 +1 @@
+Get-Module