Merge remote-tracking branch 'origin/const-qualifiers'

connector/c/include/tarantool/tnt_call.h

connector/c/include/tarantool/tnt_enc.h

connector/c/include/tarantool/tnt_io.h

connector/c/include/tarantool/tnt_iob.h

connector/c/include/tarantool/tnt_net.h

connector/c/include/tarantool/tnt_sql.h

connector/c/include/tarantool/tnt_stream.h

connector/c/include/tarantool/tnt_tuple.h

connector/c/include/tarantool/tnt_update.h

connector/c/include/tarantool/tnt_utf8.h

connector/c/tnt/tnt_buf.c

connector/c/tnt/tnt_call.c

connector/c/tnt/tnt_enc.c

connector/c/tnt/tnt_tuple.c

connector/c/tnt/tnt_update.c

connector/c/tntnet/tnt_io.c

connector/c/tntnet/tnt_net.c

connector/c/tntsql/tnt_lex.c

connector/c/tntsql/tnt_sql.c

connector/c/tntsql/tnt_utf8.c