Rewrite of summary methods (#271)

This commit implements a rewrite of the flux summary methods, using
tabulate to align and print the majority of the text. These updates fix
some lingering issues with the summary methods and will hopefully make
maintainence easier in the long term.

.travis.yml

@@ -24,7 +24,7 @@ env:
 before_install:
   - pip install pip --upgrade
   # These get cached
-  - pip install numpy scipy python-libsbml cython coveralls jsonschema six matplotlib pandas
+  - pip install numpy scipy python-libsbml cython coveralls jsonschema six matplotlib pandas tabulate
   - if [[ $TRAVIS_PYTHON_VERSION == 2* ]]; then pip install lxml glpk pep8 palettable; fi
   # Download esolver and add it to the path
   - wget https://opencobra.github.io/pypi_cobrapy_travis/esolver.gz

cobra/core/Metabolite.py

@@ -157,12 +157,15 @@ def summary(self, **kwargs):
             If given, fva should be a float between 0 and 1, representing the
             fraction of the optimum objective to be searched.
 
+        floatfmt: string
+            format method for floats, passed to tabulate. Default is '.3g'.
+
         """
         try:
             from ..flux_analysis.summary import metabolite_summary
             return metabolite_summary(self, **kwargs)
         except ImportError:
-            warn('Summary methods require pandas')
+            warn('Summary methods require pandas/tabulate')
 
 elements_and_molecular_weights = {
     'H':   1.007940,

cobra/core/Model.py

@@ -364,16 +364,18 @@ def summary(self, **kwargs):
 
         threshold: float
             tolerance for determining if a flux is zero (not printed)
+
         fva: int or None
             Whether or not to calculate and report flux variability in the
             output summary
-        round: int
-            number of digits after the decimal place to print
+
+        floatfmt: string
+            format method for floats, passed to tabulate. Default is '.3g'.
 
         """
 
         try:
             from ..flux_analysis.summary import model_summary
             return model_summary(self, **kwargs)
         except ImportError:
-            warn('Summary methods require pandas')
+            warn('Summary methods require pandas/tabulate')