Rio-tiler

------------------
- adds utils.b64_encode_img function to encode an image object into a base64 string
- add tiles profiles (jpeg, png, webp) based on https://github.com/mapnik/mapnik/wiki/Image-IO#default-output-details

Breaking Changes:
- Refactor `rio_tiler.utils.array_to_img` to return PIL image object

------------------
- only using `read_masks` for mask creation when it's needed.

------------------
- add "expression" utility function
- better nodata/mask/alpha band definition and support

Breaking Changes:
- tile functions now return an associated mask (Landsat, Sentinel, CBERS, main)
- remove nodata support in utils.image_to_array function
- add mask support in utils.image_to_array function
- utils.tile_band_worker will always return a (Band, Width, Height) array (e.g 1x256x256 or 3x256x256)

------------------
- remove aws.py sub-module (replaced by main.py)
- no default bands value for main.py tiles.

------------------
- add colormap option in `utils.array_to_img`
- add TIR (brightness temps) support
- add CBERS support
- add global file support
- add elevation encoding for mapzen
- removing internal caching
- update to rasterio 1.0a12

Breaking Changes:
- remove data value rescaling in `landsat8.tile` and `sentinel2.tile`
- fix wrong lat/grid_square value in `utils.sentinel_parse_scene_id`
- rename `utils.sentinel_min_max_worker` to `utils.band_min_max_worker`

* calculate scene bounds from multipolygons for Sentinel-1
* allow `Stripmap` beam mode for sentinel-1 dataset