Add "go-callvis" program to Go Tools section. (#1251)

go-callvis is a development tool to help visualize call graph of your Go program using Graphviz's dot format.

README.md

@@ -1272,6 +1272,7 @@ Go software and plugins.
 
 * [colorgo](https://github.com/songgao/colorgo) - A wrapper around `go` command for colorized `go build` output.
 * [gb](https://getgb.io/) - An easy to use project based build tool for the Go programming language.
+* [go-callvis](https://github.com/TrueFurby/go-callvis) - Visualize call graph of your Go program using dot format.
 * [go-pkg-complete](https://github.com/skelterjohn/go-pkg-complete) - Bash completion for go and wgo.
 * [go-swagger](https://github.com/go-swagger/go-swagger) - Swagger 2.0 implementation for go. Swagger is a simple yet powerful representation of your RESTful API.
 * [rts](https://github.com/galeone/rts) - RTS: response to struct. Generates Go structs from server responses.