Add method count for Android developers

[vaughandroid]

Android has a 64k method limit, so a lot of Android developers take method count into consideration when choosing libraries.

As this library appears to be pretty compact (especially compared to some of the bloat-ridden alternatives like Guava) highlighting the method count might encourage more use by Android developers.

[andrewoma]

Hi Chris, I'm happy to add the number to the readme if you calculate it. I don't have the android tool chain handy to generate a dex file to get an official count.

[vaughandroid]

Here's the results I get from the dexcount plugin:

• 'com.github.andrewoma.dexx:collection:0.6' = 1036 methods
• 'com.github.andrewoma.dexx:kollection:0.6' = 1213 methods

[andrewoma]

Thanks, I've added the counts to the README