Automate manifest generation

Plugin authors generate a plugin manifest using the following steps:

1. Build the plugin application using go, gb or some other development tool.
2. Run the application with the --manifest=hostName command line flag to print a manifest.
3. Add the the manifest to a .vim file (example).

These steps must be repeated every time the plugin handler registrations are changed.

This process should be automated in some way. Possible options are:

• Modify the plugin application to update a .vim file directly instead of printing the manifest to stdout.
• Create a go generate tool for updating manifests.
• Modify :UpdateRemotePlugins to work with compiled executables.

Here's one possible workflow for users:

1. User adds the plugin binary to $PATH. The go get command is one way to do this.
2. User adds line to init.vim to register binary: remote#host#RegisterExecutable('mycommand')
3. User runs :UpdateRemotePlugins

This workflow requires the addition of RegisterExecutable and modification of remote#host#UpdateRemotePlugins.

[justinmk]

was this addressed by #25 ?

[justinmk]

Remote plugin "manifest" will be removed (and not supported) after neovim/neovim#27949 is implemented.