.pytool/Plugin: Add CI plugins

https://bugzilla.tianocore.org/show_bug.cgi?id=2315

Add .pytool directory to the edk2 repository with the
following plugins.  These plugins are in a top level
directory because that can be used with all packages
and platforms.

* CharEncodingCheck
* CompilerPlugin
* DependencyCheck
* DscCompleteCheck
* GuidCheck
* LibraryClassCheck
* SpellCheck

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

.pytool/Plugin/CompilerPlugin/Readme.md

@@ -0,0 +1,17 @@
+# Compiler Plugin
+
+This CiBuildPlugin compiles the package DSC from the package being tested.
+
+## Configuration
+
+The package relative path of the DSC file to build.
+
+``` yaml
+"CompilerPlugin": {
+    "DscPath": "<path to dsc from root of pkg>"
+}
+```
+
+### DscPath
+
+Package relative path to the DSC file to build.