Add BingTileLayer to get map tiles from Bing

Based off of https://github.com/osmdroid/osmdroid/blob/master/osmdroid-third-party/src/main/java/org/osmdroid/tileprovider/tilesource/bing/imagerymetadata/ImageryMetaDataResource.java
Add /core prefix.
Merge pull request #522 from mapbox/core-prefix

Add /core prefix.
#464 - Cherrypicking and merging https://github.com/Akylas/mapbox-android-sdk/commit/ce5c46cd9710a084fe199343dab1099194898b4c
#464 - Cherrypicking and merging https://github.com/Akylas/mapbox-android-sdk/commit/82a3ffb0aa6ca2795efd19f7e75d77cd884e1cc4 to support original NPE solution in c8a5a5d8fb4220808c78201369cfaf8194c07913
#464 - Fixing checkstyle issue
Updated docs/_layouts/default.html
Updated docs/_layouts/default.html
Updated docs/_layouts/default.html
Rebuilt docs with sed changes

- Use gnu-sed for `\L` command. Closes #426
- Fix `white-space:pre-wrap` with `white-space:normal`. Ref #529
Merge pull request #531 from mapbox/gnu-sed

Rebuilt docs with sed changes
uncomment
Minor readme edits
Defer to pre-wrap
#532 - Updating installation instructions to match primary README.md
Merge remote-tracking branch 'origin/mb-pages' into mb-pages
#532 - Changing b and i to strong and code.  Making demo repo link.
#423 - Commenting out Debug Log messages for getMapTile()
#423 - Commenting out Debug Log messages
#423 - Fixing checkstyle issues