.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/DependencyCheck/Readme.md

@@ -0,0 +1,31 @@
+# Depdendency Check Plugin
+
+A CiBuildPlugin that finds all modules (inf files) in a package and reviews the
+packages used to confirm they are acceptable.  This is to help enforce layering
+and identify improper dependencies between packages.
+
+## Configuration
+
+The plugin must be configured with the acceptabe package dependencies for the
+package.
+
+``` yaml
+"DependencyCheck": {
+    "AcceptableDependencies": [],
+    "AcceptableDependencies-<MODULE_TYPE>": [],
+    "IgnoreInf": []
+}
+```
+
+### AcceptableDependencies
+
+Package dec files that are allowed in all INFs.  Example: MdePkg/MdePkg.dec
+
+### AcceptableDependencies-<MODULE_TYPE>
+
+OPTIONAL Package dependencies for INFs that have module type <MODULE_TYPE>.
+Example: AcceptableDependencies-HOST_APPLICATION.
+
+### IgnoreInf
+
+OPTIONAL list of INFs to ignore for this dependency check.