(Vcoded_charset_entity_reference_alist): New variable.

(Vcoded_charset_entity_reference_alist): New variable.
(Quse_entity_reference): New variable.
(Qd): New variable.
(Qx): New variable.
(QX): New variable.
(coding_system_description): Add description for `ccs_priority_list'.
(mark_coding_system): Mark `ccs_priority_list' in UTF-2000.
(allocate_coding_system): Initialize `ccs_priority_list' in UTF-2000.
(Fmake_coding_system): Add description about 'use-entity-reference;
setup CODING_SYSTEM_USE_ENTITY_REFERENCE (codesys).
(Fcoding_system_property): Accept `disable-composition' and
`use-entity-reference' in UTF-2000.
(struct decoding_stream): Add new member `er_counter' and `er_buf' in
UTF-2000.
(reset_decoding_stream): Initialize `str->er_counter' in UTF-2000.
(decode_coding_utf8): Decode entity-reference if
CODING_SYSTEM_USE_ENTITY_REFERENCE (str->codesys).
(char_encode_utf8): Encode non-Unicode characters as entity-references
if CODING_SYSTEM_USE_ENTITY_REFERENCE (str->codesys).
(syms_of_file_coding): Add new symbols `use-entity-reference', `d',
`x', `X'.
(vars_of_file_coding): Add new variable
`coded-charset-entity-reference-alist'.
(complex_vars_of_file_coding): Declare `disable-composition' and
`use-entity-reference' to be coding-system-properties in UTF-2000.