Modify example scripts to run on Windows

[cedrou]

The scripts run-me.sh of all examples for Marian have been slightly modified to be able to run on Windows Subsystem for Linux (WSL, aka "bash on Windows", see this page).

There are only 2 changes:

• Marian tools path are put into variables (MARIAN_TRAIN, MARIAN_DECODER, …) to allow adding the '.exe' suffix which is part of the binary name on Windows. This avoid cluttering in the rest of the script.
• As '.sh' files are not automatically bound to Bash on Windows, we need to explicitly call bash ./scripts/validate.sh in the flag --valid-script-path of marian.

[emjotde]

@cedrou The examples are meant to be run from within the Marian folder, for instance the most recent version of https://github.com/marian-nmt/marian has a gitmodule that pulls that in and places the examples folder in the marian folder. Can you make sure this works? The changed paths look like they might get in the way.

[cedrou]

The scripts should work like before. The only change I did was to move the ´/build’ part of the path that appeared at each tool call into the MARIAN variable.