Option to compile with SyncTeX using a new custom variable

[arifer612]

This PR is to solve #20 and #28

Instead of forcing the compiler to compile with SyncTeX, I introduced a new custom variable that users can tweak in their .emacs configuration or through the easy customization prompt in Emacs to tell the compiler whether SyncTeX should be used.

The second commit ties in pdf-sync from pdf-tool to follow the cursor position.

[arifer612]

Force push was simply to fix the author name.