Update CMakeLists.txt

renamed files from ldg to ledger. Don't compile ledger-context.el because it has a macro.
Merge pull request #206 from skaczor/patch-1

Update CMakeLists.txt
Apply --time-colon option only to time commodities

See #989
Merge pull request #207 from afh/pull/989

Apply --time-colon option only to time commodities