generate man pages from markdown

Fixes https://github.com/hij1nx/ldb/issues/26 and https://github.com/hij1nx/ldb/issues/31

A few things

* Original `man/ldb.1` is removed
* Generate the man page by doing `make docs`
* Generate docs, install docs and check them by doing `make test-docs`. Useful when editing the `man/ldb.1.md` file to check the final results
* Reordered command line options
* `ronn` is installed from `devDependencies` so a `npm install` is needed when writing man pages. I chose this so you aren't forced to install ronn globally