support meta commands (eg to manipulate history etc)
https://github.com/wheineman/nrpl allows using meta commands, eg:
```
> :help
:? - print this help
:help - print this help
:history - display history
:clearHist - clear history
:delete n[,m] - delete line or range of lines from history
:load filename - clears history and loads a file into history
:append filename - appends a file into history
:save filename - saves history to file
:run - run what's currently in history
:version - display the current version
:quit - exit REPL
:remove varname - remove variable
```

this would be quite useful, eg also for enabling https://github.com/AndreiRegiani/INim/issues/5 via, say, :brace=on or :brace=off

## can these be implemented as regular procs?
(and `inim` would automatically call  `from inim_special_commands as z import nil`)
eg:
```
z.help()
z.history()
#etc
```
