Be able to export the keyblob path

[perezmeyer]

The application does an usual thing: harcodes the path on which files are saved. This means that other applications/shell scripts need to know this path beforehand.

This PR:

• Creates and installs a C header file where other C/C++applications can get KEYBLOB_PATH from.
• Adds an option to print the keyblob locaiton path to stdout.
• Adds generated files entries to .gitignore.

[EstebanSannin]

I like the idea.
When I used it, I always wondered why the author hadn't implemented an option to change the keyblob_path at runtime.
Do you know if there is any reason to not do it?
Because I'm thinking of implementing it.

[perezmeyer]

@EstebanSannin I have no idea why it was designed this way. I would have used paths, but hey, there might be a reason.

Anyways, perhaps an option to pass a directory for storing the keys is a good idea.