String utils module

[uramirez8707]

Description
Adds a string_utils module that contains the following public routines and added unit tests for each:

• fms_array_to_pointer : to convert an array of strings to c_pointers
• fms_pointer_to_array : to convert an array of c_pointers back to an array of strings
• fms_sort_this: sorts an array of c_pointers in alphabetical order
• fms_find_my_string: uses a binary search to search for a string in an array of sorted c_pointers
• fms_find_unique: to find the unique of strings in array

These routines will be implemented in the diag_manager rewrite (i.e when searching the diag_yaml for a field)

To do (in a separate pr):

• Move other string-related routines to the string_utils_mods (i.e fms_c2f_string, string, str_copy, etc ...) which are currently scattered and duplicated all over FMS

How Has This Been Tested?
make check passes with intel20, gnu 9.3.0, and intel18 on skylake

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules
• New check tests, if applicable, are included
• make distcheck passes

[thomas-robinson]

To do (in a separate pr):

Move other string-related routines to the string_utils_mods (i.e fms_c2f_string, string, str_copy, etc ...) which are currently scattered and duplicated all over FMS

This should be done. You should use a USE statement in fms_mod, and make these routines public through there. Then fms_mod can depend on this instead of the other way around.

[thomas-robinson]

Can you move fms_c2f_string here, then have fms_mod use fms_string_utils_mod, only:fms_c2f_string. I think you want the dependency going the other way instead...