Step validation will happen before execution is starting

All the steps in the specification will be validated before the spec is
executing
Added build file for Windows
Added common as a submodule

This helps in managing and updating the common code
Setting GOPATH properly for windows
Adding parsing and execution for concepts.
Searching in specs directory for concepts, won't fail if it didn't find any concepts
Gandling empty concept files while parsing
minor refactoring of concept table validation
Removing * from step text
Adding placeholder {} for inline table in step value. Removing separate inline table. Inline table will be just another step arg.
Renaming special table type to tableArg
Merging master into plugins
Adding starting of execution scope plugin and some async message sending via plugin handler