rand_distr: Prepare 0.1 and 0.2 release

[vks]

For the 0.1 release, I suggest to branch off b21713a, update the changelog and publish it on crates.io.

[dhardy]

There is a problem: rand_distr's util module has use rand::distributions::hidden_export::IntoFloat; which isn't in Rand prior to 0.7, thus I cannot publish rand_distr first.

I also cannot publish rand first because it depends on rand_distr for benchmarks. So we could:

1. remove those benchmarks temporarily for 0.7.0-pre.0 then add them back
2. move the benchmarks into rand_distr
3. copy the IntoFloat code to avoid that dependency

I'm tempted just to do the simplest thing (1) for now.

[vks]

I would suggest to remove the benchmarks for now, and add them to rand_distr later.

[dhardy]

I actually implemented 3 (just for rand_distr 0.1). But still can't publish until I sort out the compatibility shim.