Ability to diff assemblies from files, directories, nuget and github (elastic#3027)

This commit adds a build target, diff, that can create a diff output of assemblies from

1. files
2. directories
3. nuget packages
4. github.amrom.workers.devmits

It uses Progress/Telerik's JustAssembly command line tool to generate an XML file of the public diffs between two assemblies, with functions implemented to transform XML to markdown and asciidoc. Since JustAssembly installation cannot be easily automated, an exception is thrown when diff is run if the tool is not installed, prompting the user with a link to download.

When specifying directories or nuget packages, the assemblies within the first path will be paired up with assemblies with the same name in the second path, and a diff will be generated for each pair.

The diff can output XML, Markdown and Asciidoc, with the latter two implemented as functions that convert the XML to a document structure.

Add skipdocs argument to be able to skip generating documentation.

Author: russcam

build/scripts/Commandline.fsx

@@ -28,6 +28,7 @@ Targets:
 * canary [apikey] [feed]
   - create a canary nuget package based on the current version if [feed] and [apikey] are provided
     also pushes to upstream (myget)
+* diff <github|nuget|dir|assembly> <version|path 1> <version|path 2> [format]
 
 NOTE: both the `test` and `integrate` targets can be suffixed with `-all` to force the tests against all suported TFM's
 
@@ -43,6 +44,7 @@ module Commandline =
     let private args = getBuildParamOrDefault "cmdline" "build" |> split ' '
 
     let skipTests = args |> List.exists (fun x -> x = "skiptests")
+    let skipDocs = args |> List.exists (fun x -> x = "skipdocs") || isMono
     let seed = 
         match args |> List.tryFind (fun x -> x.StartsWith("seed:")) with
         | Some t -> t.Replace("seed:", "")
@@ -57,7 +59,7 @@ module Commandline =
         args 
         |> List.filter (
             fun x -> 
-                x <> "skiptests" && x <> "source_serialization" && not (x.StartsWith("seed:")) && not (x.StartsWith("random:"))
+                x <> "skiptests" && x <> "skipdocs" && x <> "source_serialization" && not (x.StartsWith("seed:")) && not (x.StartsWith("random:"))
         )
 
     let multiTarget =
@@ -102,6 +104,24 @@ module Commandline =
         match Uri.TryCreate(candidate, UriKind.RelativeOrAbsolute) with
         | true, _ -> Some candidate
         | _ -> None
+        
+    let private (|IsDiff|_|) (candidate:string) =
+        let c = candidate |> toLower
+        match c with
+        | "github" | "nuget" | "directories" | "assemblies" -> Some c
+        | _ -> failwith (sprintf "Unknown diff type: %s" candidate)
+        
+    let private (|IsProject|_|) (candidate:string) =
+        let c = candidate |> toLower
+        match c with
+        | "nest" | "elasticsearch.net" | "nest.jsonnetserializer" -> Some c
+        | _ -> None     
+        
+    let private (|IsFormat|_|) (candidate:string) =
+        let c = candidate |> toLower
+        match c with
+        | "xml" | "markdown" | "asciidoc" -> Some c
+        | _ -> None 
 
     let parse () =
         setEnvironVar "FAKEBUILD" "1"
@@ -161,7 +181,28 @@ module Commandline =
             setBuildParam "esversions" esVersions
             setBuildParam "clusterfilter" "ConnectionReuse"
             setBuildParam "numberOfConnections" numberOfConnections
-            
+ 
+        | ["diff"; IsDiff diffType; IsProject project; firstVersionOrPath; secondVersionOrPath; IsFormat format] ->
+             setBuildParam "diffType" diffType
+             setBuildParam "project" project
+             setBuildParam "first" firstVersionOrPath
+             setBuildParam "second" secondVersionOrPath            
+             setBuildParam "format" format            
+        | ["diff"; IsDiff diffType; IsProject project; firstVersionOrPath; secondVersionOrPath] ->
+             setBuildParam "diffType" diffType
+             setBuildParam "project" project
+             setBuildParam "first" firstVersionOrPath
+             setBuildParam "second" secondVersionOrPath        
+        | ["diff"; IsDiff diffType; firstVersionOrPath; secondVersionOrPath; IsFormat format] ->
+             setBuildParam "diffType" diffType
+             setBuildParam "first" firstVersionOrPath
+             setBuildParam "second" secondVersionOrPath            
+             setBuildParam "format" format          
+        | ["diff"; IsDiff diffType; firstVersionOrPath; secondVersionOrPath] ->
+            setBuildParam "diffType" diffType
+            setBuildParam "first" firstVersionOrPath
+            setBuildParam "second" secondVersionOrPath         
+
         | ["temp"; ] -> ignore()
         | ["canary"; ] -> ignore()
         | ["canary"; apiKey ] ->