/*!
* @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
*/