Merge pull request #41 from briancappello/master

fix issue #40
test_abstract: adding a testcase for recent fix.
with recent changes, make version 0.4.8-git.
adding a simple check to warn the user if the ta-lib library is not installed.
minor typo fix in docstring.
support pandas.DataFrame as inputs in abstract api.
if input is pandas, output will be pandas
minor fix and a test for pandas.Series.
call the c-function with pd.Series inputs converted to np.ndarrays