to add back argument to find function

[aman-godara]

Description

Proposal (by @everythingfunctional) to add back argument to find function (as merged in PR: #433)

Often there is a back=.false. argument to functions like this (i.e. the intrinsic function index, which is very much like this one).

Prior Art

intrinsic index of fortran provides back argument.

[aman-godara]

A possible way IMO of doing this is to make a new function find_low_level and cut & paste all the code written in find_char_char to this new function. I will keep this new function private and out of the interface find. Then I can add back argument to all the 4 functions that are in find interface. So, these 4 functions will call the find_low_level in their implementation. find_low_level will not take any back argument, rather these 4 high level functions will take care of the back argument and modify the input given by user accordingly before calling find_low_level.

This is one of the possible ways of implementing back feature by building upon find_low_level function (which provides with essential features like occurrence, consider_overlapping).

[aman-godara]

aman-godara@9a8303b