Add Cyrillic and other encodings for encoding conversion.

doc/src/sgml/charset.sgml

doc/src/sgml/func.sgml

src/backend/utils/mb/conv.c

src/backend/utils/mb/conversion_procs/Makefile

src/backend/utils/mb/conversion_procs/ascii_and_mic/Makefile

...d/utils/mb/conversion_procs/ascii_and_mic/ascii_and_mic.c

...ckend/utils/mb/conversion_procs/cyrillic_and_mic/Makefile

...s/mb/conversion_procs/cyrillic_and_mic/cyrillic_and_mic.c

...backend/utils/mb/conversion_procs/euc_cn_and_mic/Makefile

...utils/mb/conversion_procs/euc_cn_and_mic/euc_cn_and_mic.c

...backend/utils/mb/conversion_procs/euc_kr_and_mic/Makefile

...utils/mb/conversion_procs/euc_kr_and_mic/euc_kr_and_mic.c

...end/utils/mb/conversion_procs/latin2_and_win1250/Makefile

.../conversion_procs/latin2_and_win1250/latin2_and_win1250.c

src/backend/utils/mb/conversion_procs/latin_and_mic/Makefile

...d/utils/mb/conversion_procs/latin_and_mic/latin_and_mic.c

...kend/utils/mb/conversion_procs/utf8_and_cyrillic/Makefile

...mb/conversion_procs/utf8_and_cyrillic/utf8_and_cyrillic.c

...ckend/utils/mb/conversion_procs/utf8_and_win1250/Makefile

...s/mb/conversion_procs/utf8_and_win1250/utf8_and_win1250.c