Add changelog for 1.0.0

[rmarianski]

@zerebubuth, @nvkelso could you review please?

[coveralls]

Coverage remained the same at 95.033% when pulling 0262f84 on changelog-1.0.0 into 75eb75a on master.

[nvkelso]

Please reorder and consolidate like:

• Generate more valid polygons and multipolygons using pyclipper library for v2 MVT compliance (but we're still not fully v2 compliant for other reasons).
• Handle edge cases where polygon buffer makes a multi-polygon, ensuring inner rings are dropped when subtracting them from the polygon would make it invalid, and not adding multipolygons as array elements for multipolygon constructor.
• Calculate area more properly by using PolyTree result from Clipper.
• Factor out polygon validity code into its own file.

[nvkelso]

You also need to update the version, which is here:

• https://github.com/tilezen/mapbox-vector-tile/blob/master/setup.py#L19

[rmarianski]

Updates in 359c80f.

[coveralls]

Coverage remained the same at 95.033% when pulling 359c80f on changelog-1.0.0 into 75eb75a on master.