ENH/REF: Additional methods for interpolate

ENH: the interpolate method argument can take more values
for various types of interpolation

REF: Moves Series.interpolate to core/generic. DataFrame gets
interpolate

add bounds_error argument. fix index overriding

add dataframe tests

hack

CLN: clean up interpolate to use blocks

ENH: Add additonal 1-d scipy interpolaters.

DOC: examples for df interpolate and a plot

DOC: release notes