Change lines of code to calculate lines of code instead of lines in file...

### What's this PR do?
Updates the way lines of code is calculated.  Currently, radon represents lines of code as the total number of lines in a file.  While I believe there are merits for choosing to use lines in file as lines in code, I believe a more accurate measure of the lines of code are all lines in the file that are not blank, docstrings, or comments.  This PR is an attempt to address this issue.

### What's next?
Much of the code is a copy and paste from my own set of scripts. Next will be to update the code and tests if we decide to move forward with the logical change.