Support sortedcontainers 2.0

This could solve
#68

intervaltree/intervaltree.py

@@ -803,7 +803,7 @@ def search(self, begin, end=None, strict=False):
             bound_end = boundary_table.bisect_left(end)  # exclude final end bound
             result.update(root.search_overlap(
                 # slice notation is slightly slower
-                boundary_table.iloc[index] for index in xrange(bound_begin, bound_end)
+                boundary_table.keys()[index] for index in xrange(bound_begin, bound_end)
             ))
 
             # TODO: improve strict search to use node info instead of less-efficient filtering
@@ -822,7 +822,7 @@ def begin(self):
         """
         if not self.boundary_table:
             return 0
-        return self.boundary_table.iloc[0]
+        return self.boundary_table.keys()[0]
 
     def end(self):
         """
@@ -832,7 +832,7 @@ def end(self):
         """
         if not self.boundary_table:
             return 0
-        return self.boundary_table.iloc[-1]
+        return self.boundary_table.keys()[-1]
 
     def range(self):
         """

setup.py

@@ -59,7 +59,7 @@ def run_tests(self):
 setup(
     name='intervaltree',
     version=version_info['version'],
-    install_requires=['sortedcontainers'],
+    install_requires=['sortedcontainers >= 2.0, < 3.0'],
     description='Editable interval tree data structure for Python 2 and 3',
     long_description=doc.get_rst(),
     classifiers=[  # Get strings from http://pypi.python.org/pypi?%3Aaction=list_classifiers