Update 'buffer' to v5.x

Browser support

buffer v5.x drops support for IE8-10.

This allows us to remove the Object implementation and rely on a single fast implementation based on Typed Arrays, greatly simplifying the maintanence of the buffer package.

Typed arrays are supported by 97.08% of the U.S. browser market and 92.02% of the global browser market. Source: http://caniuse.com/#search=typed This number continues to increase at a steady rate each month.

If IE8-10 support is critical to your web app, you can continue to rely on browserify v13.

Bundle size

This change shrinks the size of buffer modestly.

55.1kb -> 52.1kb (full size, with comments) 7.0kb -> 6.7kb (minified, gzipped)

Bug fixes

buffer v5.x contains several important fixes including:

• https://github.com/feross/buffer/commit/3639a98a97888477d1bc6b335fb27b48b550a751
• https://github.com/feross/buffer/commit/4e5c4526f4c29201fa833a89d8fe2bf15ebb18e5
• https://github.com/feross/buffer/commit/99491d2f16d6f20940dd86ed2cb6e8629181723e

Semver

This should be released as semver major.