Running current file

[lpoto]

Add default generators that run the current file. For example, a generator should check whether the current file contains a main function, and generate a task for running it, if it does (this would be useful for filetypes such as c, c++, java).

Something like this is currently already implemented for Go default generators
(It generates a task for a file only if it contains main package and main function), and for Lua.