Igv tools stdout

Support writing output to stdout, instead of output file. This is done by using the string "stdout" for the output file.

Only works for "sort" (output same format as input) and "count" (output is wiggle format) command. It could be done for "index" but I'm not sure how useful that would be (since the index and source file need to co-exist).

Writing TDF files to a stream is not as easy because the index position is only known once the whole file is generated. So the output needs to be buffered.