Appends a subsequence of the specified character sequence to this Appendable.

An invocation of this method of the form out.append(csq, start, end) when csq is not null, behaves in exactly the same way as the invocation

     out.append(csq.subSequence(start, end))

Parameters:

csq     The character sequence from which a subsequence will be appended. If csq is null, then characters will be appended as if csq contained the four characters "null".

start     The index of the first character in the subsequence

end     The index of the character following the last character in the subsequence

Returns: A reference to this Appendable

Exceptions:

IndexOutOfBoundsException If start or end are negative, start is greater than end, or end is greater than csq.length()

IOException If an I/O error occurs

`csq`		The character sequence from which a subsequence will be appended. If `csq` is `null`, then characters will be appended as if `csq` contained the four characters `"null"`.
`start`		The index of the first character in the subsequence
`end`		The index of the character following the last character in the subsequence

`IndexOutOfBoundsException`		If `start` or `end` are negative, `start` is greater than `end`, or `end` is greater than `csq.length()`
`IOException`		If an I/O error occurs