embed raw string for plain text files

To embed the raw string for plain text files, which would make it smaller, also easier for manual modification.


Actually it might also be used for binary data, as `\xAA` is usually shortter than `, DD`, but there are encoding issues, especially closure compiler always assumes a utf 8 encoding.

Another idea is to use base64 encoding, it'll increase only a third of the file size, but array uses three times as much as the original file.


Passed all tests that use `--embed-file`:

test_cube2md5
test_fgetc_unsigned
test_fgets_eol
test_fscanf
test_mmap_file

other.test_ungetc_fscanf
other.test_embed_file
other.test_embed_file_dup
other.test_fs_stream_proto

browser.test_sdl_audio