Added new function mean_alpha and tests

This function allows to compute the mean alpha diversity data at a given
rarefaction depth.
Updated script to handle collated alpha data

Collated alpha diversity files can now be used with this script, the
user is now able to specify a given depth to get the mean of the values
added to the mapping file.
Merge pull request #596 from ElDeveloper/collated_alpha_map

Collated alpha map
Adding functionality to calculate linear distance from a latitute/longitud point
Fixing a missing credit
Fixing issues from pull request
Fixing wrong evaluation of max/min lat/long
Fixing error message for lat/long evaluation
Merge pull request #602 from antgonza/lat_long_distance

Adding functionality to calculate linear distance from Latitude/Longitude point
Fixing error with distance_matrix_from_mapping.py in Clout
Merge pull request #607 from antgonza/fix_for_distance_matrix_from_mapping_in_clout

Fixing error with distance_matrix_from_mapping.py in Clout