Make begin_read() and end_read() private
Make find_executable() static
Use a run() method instead of a functor
Pass the process to run() instead of the constructor

Also remove the (rarely used) possibility to pass process arguments as an
array of strings instead of a space separated list.
Prefix member variables with "m_"
Run the capturing in a separate thread and add a test program

The test program simulates the use from within Inno Setup and thus uses
__stdcall to undecorated function names. Also, as a GUI program, it does
not allocate a console.
Work-around Pascal Script passing empty PAnsiChar strings as NULL pointers
Return the running state when starting to capture a process
To be safe, set the captured text to NULL even if returning "false"
In the test program, add BEGIN / END markers for the captured output
Split the capturing process into begin / end functions for clarity
Merge branch 'master' of github:sschuberth/is-procap