ledger-mode: define and use a syntax table so that comments are handled properly
ledger-mode: define and use a syntax table so that comments are handled properly

Specifically, functionality which uses syntax-ppss to detect comments
needs the syntax table to be aware of them. A prime example is
goto-address-prog-mode.

This commit adds a basic syntax table for this purpose.

jwakely/ledger,ledger/ledger,paulbdavis/ledger,ledger/ledger,paulbdavis/ledger,jwakely/ledger,duncanmortimer/ledger,paulbdavis/ledger,jwakely/ledger,paulbdavis/ledger,afh/ledger,jwakely/ledger,duncanmortimer/ledger,duncanmortimer/ledger,afh/ledger,jwakely/ledger,duncanmortimer/ledger,duncanmortimer/ledger,afh/ledger,afh/ledger,paulbdavis/ledger,jwakely/ledger,ledger/ledger,paulbdavis/ledger,ledger/ledger,duncanmortimer/ledger,paulbdavis/ledger,jwakely/ledger,duncanmortimer/ledger,afh/ledger,ledger/ledger