Dynamically build list of available functions

[pgporada]

Currently, the way to use this code appears to be having two terminals open. One session with the API client and another session looking at the case statements in main.go to see a list of available functions. This feels obtuse.

It would be nice to have the following or something like it

$ ./proxmox-api-go -h
Usage of ./proxmox-api-go:
  -function_list

$ ./proxmox-api-go -function_list
createQemuSnapshot
listQemuSnapshot
rollbackQemu
sshforward
sshbackward
...