Arcas crashes when no command line options are given

[BlairArchibald]

Arcas currently crashes instead of exiting cleanly when you don't specify any options on the cmdline:

(env) blair@athos:~/sandbox/Arcas/bin$ python arcas_scrape
Traceback (most recent call last):
  File "arcas_scrape", line 45, in <module>
    url = api.create_url_search(parameters)
  File "/home/blair/sandbox/Arcas/src/arcas/tools.py", line 30, in create_url_search
    url += parameters[0]
IndexError: list index out of range