Add sesh_osapi_pselect function
Add FileDescriptorSet abstract class
Add RealFileDescriptorSet class
Add Api::createFileDescriptorSet function
Add SignalNumber type alias
Add SignalNumberSet abstract class
Add RealSignalNumberSet class
Add Api::createSignalNumberSet function
Add RealApi::INSTANCE constant
Add Api::pselect function
Merge pull request #78 from magicant/feature/select

Add OS API wrapper for pselect