In a future assignment, you are going to write a program which reads
some input, does some manipulations, and produces output in another file.
Right now, you are going to write a function which will be useful to you
in that assignment, which takes the input filename, and produces the output
file name. The output file name should be the same as the input file name
with ".counts" on the end.  So, for example, if the input filename (inputName)
is "input.txt", your function should return "input.txt.counts".

Note that your function needs to use malloc to allocate memory to hold
the string that it will return as its answer.

Your function should have the following signature:

 char * computeOutputFileName(const char * inputName)

and you should write it in the outname.c file.
You can make and test with the main function found in outname_test.c.
As always, be sure your program valgrinds cleanly.