Replace dep with Go module

This repo currently uses dep to manage its package dependencies. The dep functionality is now legacy and has been replaced with Go modules. The repo should be converted to a Go module.

In addition, this repo uses a makefile to build its executable. It appears that this is unneeded. Normal use of Go tooling should be sufficient to build its executable.

Start by inspecting the repository's dep configuration and Makefile, then check how the executable is currently built and how Go modules are initialized. Convert the dependency setup to a Go module and verify that standard Go tooling builds the executable without the Makefile or dep workflow.

Written by the indexing model from the issue text.