Adding support for homebrew install

[sfdye]

Relates #94

Homebrew/homebrew-core#33087

I have created a new formula in homebrew-core and waiting for the upstream to review and merge (hopefully). Once this is accepted, one is able to install the plugin by:

brew install wechat-plugin

[sfdye]

@TKkk-iOSer It seems in order for the new brew formula to be accepted, we need to build the framework from source. There are some issues with Cocoapods on brew's build system, and one possible solution is to switch from Cocoapods to Carthage. I am not familiar with macOS dev, do you think the amount of work is manageable and worth it?

See an example with using Carthage:

repo: https://github.com/mas-cli/mas
brew formula: Homebrew/homebrew-core#33104
PR to switch from Cocoapods to Carthage: mas-cli/mas#169

[sfdye]

An alternative way is we maintain an unofficial tap

[TKkk-iOSer]

Carthage 的话倒不是很熟悉，之后我再去看下

[sfdye]

好的，这个mas-cli的PR已经merge了:
Homebrew/homebrew-core#33104

看来如果想被homebrew官方收录就必须换到Carthage, 我看了这个project的dependency不多，应该难度还ok。如果需要帮忙可以跟我说。