Adds a basic command line interface

Closes #68 (closed) by giving a simple interface to set the log-level (unless set at the script level) and whether or not to use cached data.

You can check what is available with

$ python basic_tutorial.py --help

for example.

examples/injection_examples/basic_tutorial.py

@@ -14,7 +14,7 @@ time_duration = 4.
 sampling_frequency = 2048.
 outdir = 'outdir'
 label = 'basic_tutorial'
-tupak.utils.setup_logger(outdir=outdir, label=label, log_level="info")
+tupak.utils.setup_logger(outdir=outdir, label=label)
 
 np.random.seed(170809)