Call out non-existent paths when attempting to archive

[ethall]

Subject of the issue

Syphon tries to create a lock file without checking whether the target directory exists.

Your environment

• Python 3.6.6
• Syphon 0.1.1

Steps to reproduce

1. Create a temporary archive directory (example_archive in subsequent steps).
2. Initialize the directory for Syphon use:

$ syphon init example_archive blah

3. Try to archive data from a directory that does not exist:

$ syphon archive -d .\fake\location\*.csv data

Expected behaviour

An understandable error message should be returned.

Actual behaviour

The following is printed:

Traceback (most recent call last):
  File "C:\Python36\lib\runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "C:\Python36\lib\runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "C:\Source\forked\syphon\syphon\__main__.py", line 99, in <module>
    bootstrap(argv)
  File "C:\Source\forked\syphon\syphon\__main__.py", line 15, in bootstrap
    exit(_main(args))
  File "C:\Source\forked\syphon\syphon\__main__.py", line 84, in _main
    archive(this_context)
  File "C:\Source\forked\syphon\syphon\archive\archive.py", line 45, in archive
    lock_list.append(lock_manager.lock(split(data_list[0])[0]))
  File "C:\Python36\lib\site-packages\sortedcontainers\sortedlist.py", line 641, in __getitem__
    raise IndexError('list index out of range')
IndexError: list index out of range