Remove unneeded call to Repository#root_ref in #log

See merge request !117

From our monitoring data, it seems that Repository#root_ref can be slow
sometimes (probably because it involves iterating over all branches),
and there's no need to have it in the `default_options` hash since
a similar effect is achieved in `actual_ref = options[:ref] || root_ref`
below, and subsequent calls don't need a `:ref` key in the passed
options.

Optimize fetch of the author and committer of a Rugged commit

Closes #26

See merge request !116

We're using Forwardable so we need to require it

See merge request !92

Compare returns an empty collection of commits on nil refs

See merge request !114

Write .gitattributes in binary mode to prevent Rails from converting ASCII-8BIT to UTF-8

This avoids Sidekiq errors in the PostReceive task due to .gitattributes files having ISO-8859 characters, such as:

```
Encoding::UndefinedConversionError: "\xC3" from ASCII-8BIT to UTF-8
```

Closes gitlab-org/gitlab-ce#20647

See merge request !115

Closes gitlab-org/gitlab-ce#20647

Lazy load compare commits

See merge request !113

Clean up local branches after creation to make rspec pass



See merge request !112

Use an exact rubocop-rspec version that's compatible with ruby 2.1

... otherwise it breaks rubocop and rspec builds.

See merge request !110

Add deltas_only option for DiffCollection

See merge request !109

It helps avoiding loading the actual patch (which can consume lots of
memory) when not needed.

Improve performance of a decorated DiffCollection instance

See merge request !108

Add forwardable require to Repository

This class makes use of the Forwardable stdlib but didn't require it
explicitly.

See merge request !107

This class makes use of the Forwardable stdlib but didn't require it
explicitly.

Test against Ruby 2.3 and use caching of gems

See merge request !106

Expose tags git object sha (if it's an annotated tag)

Closes #24

See merge request !104

Refactor Refs to preserve their target objects instead of just a string representation

Notice that in `spec/tag_spec.rb` I changed the sha because previously they
referenced the tag annotation commit. With the refactor, the sha must be the one
of the commit that the tag actually points at.

Closes #22

See merge request !103

Notice that in `spec/tag_spec.rb` I changed the sha because previously they
referenced the tag annotation commit. With the refactor, the sha must be the one
of the commit that the tag actually points at.

Handle collapsable DiffCollection

We want to give the user the opportunity to see more files while preserving safe limits on rendering diffs so files bigger than 10KB (we consider too large 100KB) their lines are not taking into account to decide if the collection overflow and you can decide if you want to expand them on click or no. And those files will be collapsed by default (they are just quite big).

Besides to keep good performance we start collapsing all the files since we are over the safe limits (what we used before as hard limits). So we can start measuring rendering files with expand links and in the future move to higher the safe limits maybe.

To do that you have to methods `collapsed?` and `collapse` which means if it's quite large and the other if the collection collapsed it when iterated as a whole.

It's quite similar to the `too_large`concept but give us a little bit more flexibility.

Related with: https://gitlab.com/gitlab-org/gitlab-ce/issues/19820

See merge request !101

We want to give the user the opportunity to see more
files while preserving safe limits on rendering diffs
so files bigger than 10KB (we consider too large 100KB)
their lines are not taking into account to decide
if the collection overflow and you can decide if
you want to expand them on click or no.

To keep good performance we start collapsing all
the files since we are over the safe limits.

To do that you have to methods `collapsed?` and
`collapse` which means if it's quite large and the
other if the collection collapsed it when iterated
as a whole.

It's quite similar to the `too_large`concept but
give us a little bit more flexibility.