Add count() or len() method for space

[kbelyavs]

It would be great to align space interface with TNT submodule box.space
For example, to get number of values, I have to use something like this:
len(space.select()) which I believe is not efficient

[Totktonada]

You can use <connection object>.call('box.space.<space name>:len') or <connection object>.eval('return box.space.<space name>:len()') if the relevant access is granted.

Anyway, while there is no such request in tarantool's binary protocol, we can't do anythyng more elegant in the connector.

[Totktonada]

(Updated my answer above.)