Address the following in the documentation:

put_bytes vs put_string
put_string vs put_cstring
rewind! only affects read position
put_symbol and put_string accepting null bytes in input strings/symbols
put_symbol writing the symbol as string

Repair the following bugs:

Providing a string of length > 1 to put_byte writes only the first byte to the buffer
Providing a string of length 0 to put_byte reads undefined data, writes it to buffer and advances write position by 1
replace_int32 performs no range check on position argument, can overwrite arbitrary data not belonging to the buffer
put_symbol truncates symbols containing null bytes

Add tests as needed.