CocoaPods podspec for v1.1.0

[banjun]

refs #2 #4

added a CocoaPods podspec file pointing to v1.1.0 and LICENSE file. (LICENSE file is required for pod validation.)

You can publish this pod after merge, according to the guide:
http://guides.cocoapods.org/making/getting-setup-with-trunk.html

1. signing up: pod trunk register YOU@example.com 'YOUR NAME' --description='macbook air'
2. sending to the Specs repo: pod trunk push Socket.IO-Client-Swift.podspec

[banjun]

pod trunk push validation may fail with this podspec like below..., as v1.1.0 tag does not contain LICENSE file.

 -> Socket.IO-Client-Swift (1.1.0)
    - WARN  | [iOS] Unable to find a license file

in the case, please tag after the merge commit and modify podspec's s.source line.
for example, :tag => 'v1.1.0' -> :tag => 'v1.1.0-pod'

[nuclearace]

@banjun I think I did it. But I have no idea.

[banjun]

@nuclearace thank you for merging! 👍

I confirmed we can now pod search socket.io, pod install with pod 'Socket.IO-Client-Swift', and add s.dependency 'Socket.IO-Client-Swift', '~> 1.1' to another pod!

[nuclearace]

@banjun if you want to update the README to include a CocoaPods install section, I'll merge it.