Removed 'string' from 10 stringtools function names.

Changed the names of the following functions:

    stringtools.capitalize_string_start() ==>
    stringtools.capitalize_start()

    stringtools.is_dash_case_string() ==>
    stringtools.is_dash_case()

    stringtools.is_lower_camel_case_string() ==>
    stringtools.is_lower_camel_case()

    stringtools.is_snake_case_string() ==>
    stringtools.is_snake_case()

    stringtools.is_space_delimited_lowercase_string() ==>
    stringtools.is_space_delimited_lowercase()

    stringtools.is_upper_camel_case_string() ==>
    stringtools.is_upper_camel_case()

    stringtools.pluralize_string() ==>
    stringtools.pluralize()

    stringtools.string_to_accent_free_snake_case() ==>
    stringtools.to_accent_free_snake_case()

    stringtools.string_to_space_delimited_lowercase() ==>
    stringtools.to_space_delimited_lowercase()

    stringtools.strip_diacritics_from_binary_string() ==>
    stringtools.strip_diacritics()

CHANGE: should be noted in the 2.15 change log.