.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/LibraryClassCheck/Readme.md

@@ -0,0 +1,25 @@
+# Library Class Check Plugin
+
+This CiBuildPlugin scans at all library header files found in the `Library`
+folders in all of the package's declared include directories and ensures that
+all files have a matching LibraryClass declaration in the DEC file for the
+package. Any missing declarations will cause a failure.
+
+## Configuration
+
+The plugin has a few configuration options to support the UEFI codebase.
+
+``` yaml
+"LibraryClassCheck": {
+    IgnoreHeaderFile: [],  # Ignore a file found on disk
+    IgnoreLibraryClass: [] # Ignore a declaration found in dec file
+}
+```
+
+### IgnoreHeaderFile
+
+Ignore a file found on disk
+
+### IgnoreLibraryClass
+
+Ignore a declaration found in dec file