Improves histogram buckets over the default set

[bdarfler]

This is an attempt at a usable set of buckets for a wide range of metrics

Which problem is this PR solving?

Fixes #115

As noted in the issue, the default buckets in the go client are as follows:

DefBuckets = []float64{.005, .01, .025, .05, .1, .25, .5, 1, 2.5, 5, 10}

… and from the docs …

DefBuckets are the default Histogram buckets. The default buckets are tailored to broadly measure the response time (in seconds) of a network service. Most likely, however, you will be required to define buckets customized to your use case.

Additionally from the docs …

Buckets defines the buckets into which observations are counted. Each element in the slice is the upper inclusive bound of a bucket. The values must be sorted in strictly increasing order. There is no need to add a highest bucket with +Inf bound, it will be added implicitly. The default value is DefBuckets.

In the end, the cache_entries metric therefore always ends up in the implicit +inf bucket and makes the metric nearly useless. You just know your cache_entries are more than 10.

For example "your stuff is more than 10!":

[akasprzok]

I'm on board with this!

[robbkidd]

These buckets appear to be more better.