Method init

This method allocates and initializes the preconditioner p, according to the preconditioner type chosen by the user.

`contxt`	`type(psb_ctxt_type), intent(in)`.
	The communication context.
`ptype`	`character(len=*), intent(in)` .
	The type of preconditioner. Its values are specified in Table 1.
	Note that strings are case insensitive.
`info`	`integer, intent(out)`.
	Error code. If no error, 0 is returned. See Section 7 for details.