Replace 6.0-to-6.7.md with 6.0-to-6.8.md

rake setup

Add alias `rake setup` to `rake gitlab:setup`
Mention in developer docs

 Add uniq db index on project_id+iid

Because:
* its faster
* it solves problem with repeating iid's in one project

gitlab.yml description Typo

Adjust MySQL limits for existing installations

Tests for fog

Fix grammar and typos in Webhooks help

This MR gets rid of some typos and wrong grammar in [help/web_hooks](https://gitlab.com/help/web_hooks).

Fix syntax highlighting

Fix diff height

Bump gitlab shell

allow passing user's email address in custom Gravatar urls

Some custom avatar systems use the user's email address rather than its hash. This merge request will allow the administrator to configure gitlab-ce to use the user's email address gravatar.plain_url and  gravatar.ssl_url in the config file like this:

```
gravatar:
    enabled: true
    plain_url: "http://company.com/avatar/?mail=%{email}&size=%{size}"
    ssl_url: "https://company.com/avatar/?mail=%{email}&size=%{size}"
```

It's a only a 2 word patch.

LDAP Configuration Fix

This fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/180 in new installations of version 6.8 (installations upgraded from 6.7 still have the issue, however).

Fix code block that doesn't render correctly in doc.gitlab.com

Probably fixes https://gitlab.com/gitlab-com/doc-gitlab-com/issues/6

Add markdown styleguide.