Where queries should support "in" correctly when the left hand is a string

[wasade]

$ redbiom search metadata "beer | wine where 'fermented' in sample_type"
Traceback (most recent call last):
  File "/Users/mcdonadt/miniconda3/envs/redbiom/bin/redbiom", line 11, in <module>
    load_entry_point('redbiom', 'console_scripts', 'redbiom')()
  File "/Users/mcdonadt/miniconda3/envs/redbiom/lib/python3.5/site-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/Users/mcdonadt/miniconda3/envs/redbiom/lib/python3.5/site-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/Users/mcdonadt/miniconda3/envs/redbiom/lib/python3.5/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/mcdonadt/miniconda3/envs/redbiom/lib/python3.5/site-packages/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/mcdonadt/miniconda3/envs/redbiom/lib/python3.5/site-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/mcdonadt/miniconda3/envs/redbiom/lib/python3.5/site-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/Users/mcdonadt/ResearchWork/software/sequence-search/redbiom/commands/search.py", line 87, in search_metadata
    for i in redbiom.search.metadata_full(query, categories):
  File "/Users/mcdonadt/ResearchWork/software/sequence-search/redbiom/search.py", line 56, in metadata_full
    obs = set(redbiom.where_expr.whereeval(q, get=get).index)
  File "/Users/mcdonadt/ResearchWork/software/sequence-search/redbiom/where_expr.py", line 160, in whereeval
    result = eval(ast.dump(formed))
  File "<string>", line 1, in <module>
  File "/Users/mcdonadt/ResearchWork/software/sequence-search/redbiom/where_expr.py", line 135, in Compare
    left = op(left, comp)
  File "/Users/mcdonadt/ResearchWork/software/sequence-search/redbiom/where_expr.py", line 91, in _in
    return left[left.isin(right)]
AttributeError: 'str' object has no attribute 'isin'
``