fetch attribute parser. mail body text with dummy encoding is encoded to utf-8 to search text.
search key parser. unit test utility function is modified for charset search parameter.
search key parser. charset parameter unit test for BODY keyword.
search key parser. charset parameter unit test for TEXT keyword.
Merge branch 'unit_test' into search_charset
protocol decoder. charset parameter unit test for search command with BODY search key.
protocol decoder. charset parameter unit test for search command with TEXT search key.
search key parser. refactored internal function.

new shift_string_value function.
new shift_date_value function.
new shift_octet_size_value function.
obsoleted str2time function that is merged to shift_string_value fcuntion.
Merge branch 'search_charset'