Version 2.0.0

- Complete split and reorganization of code into separate `autoload/` and `plugin/` modules
- Default key maps now use direct `m` trigger instead of `<Leader>m` (fully-configurable, from no mapping at all, to old `<Leader>m` style maps, to new and sleek `m` maps)
- Easily toggle highlighting of marked lines
- Remove old signs for marks that are doubled up (Benjamin Thomas)
- Use noremap instead of map to avoid space mapping issues
- Added option to disable default key-mapping entirely (Jonathan Geddes)
- Correctly show marks on first line
- Correctly behavior to avoid complaints due to Vim patch 7.4.275