Default output directory

[afrubin]

Program crashes with a FileNotFoundError when no destination is specified. It should default to a path of the form <location of input file>/<program mode>.

$ mavedb-convert enrich E4B_Dataset_S1.xlsx --wtseq ../E4B_wt.fa --score_column nscor_log2_ratio
[INFO] 2018-11-26 11:23:43,687 base Checking read permission for 'E4B_Dataset_S1.xlsx'
[INFO] 2018-11-26 11:23:43,688 base Creating directory ''
[ERROR] 2018-11-26 11:23:43,688 main An error occured during conversion.
Traceback (most recent call last):
  File "/Users/rubin.a/Code/mavedb-convert/mavedbconvert/main.py", line 194, in main
    enrich.Enrich(**kwargs).convert()
  File "/Users/rubin.a/Code/mavedb-convert/mavedbconvert/enrich.py", line 33, in __init__
    input_type=input_type,
  File "/Users/rubin.a/Code/mavedb-convert/mavedbconvert/base.py", line 90, in __init__
    os.makedirs(dst, exist_ok=True)
  File "/Users/rubin.a/.pyenv/versions/3.6.5/lib/python3.6/os.py", line 220, in makedirs
    mkdir(name, mode)
FileNotFoundError: [Errno 2] No such file or directory: ''