chainladder 0.6.1

Bug fixes:

• Corrected a bug where TailConstant couldn't decay when the contant is set to 1.0
• #71 Fixed issue where ``Pipeline.predictwould not honor thesample_weight` argument

Enhancements:

• #72 Added drop method to Triangle similar to pd.DataFrame.drop for dropping columns
• Added xlcompose yaml templating
• #74 Dropped link ratios now show as ommitted when callinng link_ratio on a Development transformed triangle
• #73 Triangle.grain now has a trailing argument that will aggregate triangle on a trailing basis