feat: Allow block on tags_context and extra_context

[rivayama]

This makes tags_context and extra_context block receivable and it defines a scope for the tags/extra.

Before:

posts.each do |post|
  Raven.tags_context(post_id: post.id)
  # do something
end
Raven.context.tags.delete(:post_id)

After:

posts.each do |post|
  Raven.tags_context(post_id: post.id) do
    # do something
  end
end

[HazAT]

THX!

[tycooon]

Hi, I added a comment here: 0b25744. Please take a look.

UPD: Ah, I see that #931 is already created.

[philipbjorge]

@rivayama -- Is there a specific reason that we didn't add this capability for user context?
Just wondering or if this is a good opportunity for me to make a PR 😉