fn() isalpha

Check if character is a upper or lowercase letter

/*!
 * @fn isalpha
 * 
 * @headerfile <cctype>
 * 
 * @brief Check if character is a upper or lowercase letter
 * 
 * @signature bool isalpha(c);
 * 
 * @param[in] c The character to be checked. Type: <tt>int</tt>
 * 
 * @return bool <tt>true</tt> (non-zero) if <tt>c</tt> is a character.
 * 
 * @section Remarks
 * 
 * This is non-SeqAn, plain c and listed for completeness.
 * 
 * @see http://www.cplusplus.com/reference/clibrary/cctype/isalpha/
 * @see http://www.cppreference.com/wiki/string/character_classes
 * @see FileFormatTokenization#readLetters
 */