Fix bashplotlib dependency

Makes this an optional module, adds it to the requirements and README.md

README.md

@@ -49,8 +49,12 @@ $ git clone git@gitlab.aei.uni-hannover.de:GregAshton/PyFstat.git
 * [emcee](http://dan.iel.fm/emcee/current/)
 * [corner](https://pypi.python.org/pypi/corner/)
 * [dill](https://pypi.python.org/pypi/dill)
+
+*Optional*
 * [tqdm](https://pypi.python.org/pypi/tqdm)(optional), if installed, this
   provides a useful progress bar and estimate of the remaining run-time.
+* [bashplotlib](https://github.com/glamp/bashplotlib), if installed, presents
+  a histogram of the loaded SFT data
 
 For an introduction to installing modules see
 [here](https://docs.python.org/3.5/installing/index.html). If you are using

pyfstat/core.py

@@ -249,7 +249,7 @@ class ComputeFstat(object):
                 from bashplotlib.histogram import plot_hist
                 print('Data timestamps histogram:')
                 plot_hist(SFT_timestamps, height=5, bincount=50)
-            except IOError:
+            except ImportError:
                 pass
         if len(detector_names) == 0:
             raise ValueError('No data loaded.')

requirements.txt

@@ -5,5 +5,6 @@ emcee
 corner
 dill
 tqdm
+bashplotlib