Execute a command at the remote end and allocate a channel for it.
session
An SSH connection link identifier, obtained from a call to ssh2_connect().
command
pty
env
env
may be passed as an associative array of
name/value pairs to set in the target environment.
width
Width of the virtual terminal.
height
Height of the virtual terminal.
width_height_type
width_height_type
should be one of
SSH2_TERM_UNIT_CHARS or
SSH2_TERM_UNIT_PIXELS.