feature: support sniffer block usage

[dsalahutdinov]

[WIP] for #27

Hi!
May be i did not get the idea properly, so i have some questions:

1. Do we need to support the default Sniffer without any capture block?
2. Do we need to support nested capture (as it is done now)
3. What way we will configure local capture sniffer. This doesn't look good

config = Confgi.new |config|
  config.enabled!
  ...
end
captured = Sniffer.capture(config) do
  # make some http requests
end

[aderyabin]

Sorry, for the misconception.
For example, we have a default config:

Sniffer.config do |c|
  c.logger = Logger.new($stdout)
end

And I want to capture requests in two different blocks of code:

sniffer1 = Sniffer.new(logger: Logger.new('foo.log'), enabled: true) # it merges with default config
# some code
sniffer1.disable!

# another code

sniffer2 = Sniffer.capture(logger: Logger.new('bar.log') do #sniffer2 enabled
# some requests
end #sniffer2 disabled

Yes, I think we have to support nesting (it's a challenge). It writes the request to both sniffer instances:

sniffer1 = Sniffer.new(logger: Logger.new('foo.log'), enabled: true)
# requests log into sniffer1
sniffer2 = Sniffer.capture(logger: Logger.new('bar.log') do #sniffer2 enabled
# requests log into both sniffers
end
# requests log into sniffer1
sniffer1.disable!

[dsalahutdinov]

Hi, please take a look, PR is still in WIP (ugly code somwhere, lack of the tests), but want to discuss the idea

1. Have the default sniffer, which is disabled by default (works as it worked before)
2. Calling capture - enables another instance, which is enabled by default and capturing all the requests inside the block

So i made:

• the Instance class for containing the data (making Sniffer class is not easy, because it is module everywhere)
• Sniffer module singleton methods are the one entrypoint to work with all the sniffer instances (the api is mostly the same, as it was), but methods like enabled?, store and log - works with all the nested instances depending of their's enable status

In usual case works like was before

[dsalahutdinov]

One thing I missed, it that we don't want to have default sniffer (without creating at least one instance - the sniffer should not work)

[dsalahutdinov]

Made some changes:

1. extracted sniffer instance to capture class, where all the stuff is saved:

capture = Sniffer.new
puts capture.data

2. no default instance is enables, so to start sniffer you need to instantiate is

capture = Sniffer.new(enabled: true)

3. Capture method with block allows to add more sniffer:

capture = Sniffer.capture(enabled: true) do
  # make http requests

  # supports for nesting
  nested = Sniffer.capture(enabled: true, logger: HipsterLogger.new) do
    # capture to this, outer, and to default (according to enable settings)
  end
end

Wait for your review @aderyabin

[dsalahutdinov]

@aderyabin , could you please review

[aderyabin]

Already defined in gemspec file