range to range raw

[maurolacy]

Closes #460.

Lots of changes, but basically renaming range to range_raw, and range_de to range.

• Deprecates range in favour of range_de, keeping range as range_raw.
• Keeps prefix_de as prefix, and remove the currents prefix. That is, no prefix_raw impl, which will be confusing. That implies making range_raw work with / over prefix_de.
• Migrates the code in contracts to take advantage of the new key deserialization when useful.
• Improve traits segregation over Map and Prefix range-related methods, so that trait bounds are enforced only when strictly needed. (out of scope for this PR)

Could have chosen to provide two prefix functions, prefix and prefix_raw, but opted instead to provide one prefix with two ranges over it, range and range_raw, for simplicity of use. The only drawback is that if you want to prefix, you need to provide key deserialization impls for the involved keys, even if / when using only range_raw. This is reasonable IMO, as we are providing many of those impls already.

Most interesting stuff is in the contracts, where we leverage the new key deserialization functionality for clarity and convenience.

[ethanfrey]

I like the idea.
Have not done a thorough review

[ueco-jb]

lgtm