URL tweaking to reference exact relation hooks. Dropped some notes regarding bugs that have been resolved for some time.

Note regarding the bug notice drops:
1. In authors-charm-config.md, there is a reference to [juju-core bug #1194945](https://bugs.launchpad.net/juju-core/+bug/1194945) regarding issues with default values and type mismatching. This bug was resolved in 1.15.0, so it doesn't make sense to have the notice / warning about it.
2. In authors-hook-environment.md, there is a reference to [juju-core bug #1223325](https://bugs.launchpad.net/juju-core/+bug/1223325) regarding the inability to specify logging levels as well as the arg being ignored. This bug was resolved in 1.17.2, so it doesn't make sense to have the notice about it.

Other changes:
1. Note in authors-charm-hooks was broken, syntax changed to reflect Juju markdown syntax.
2. Changed authors-charm-hooks references to hooks, such as -joined, to make it more obvious / stand out more against the paragraphs and walls of text.
3. Dropped authors-hook-kinds since it was just an outdated version of authors-charm-hooks. If anyone opposes this, the least that we can do is simply copy authors-charm-hooks.md to authors-hook-kinds.md. As a result of dropping this file, all references to it now reference authors-charm-hooks and any necessary direct link to a hook. Example: in authors-charm-upgrades, in the Forced charm upgrades section the reference to the upgrade-charm hook has been updated to directly point to the upgrade-charm hook section in authors-charm-hooks.
4. Fixed code reference in authors-charm-store.md
5. authors-charm-writing.md has gotten some tweaking, mainly a lack of a period and ending parenthesis. I also noticed that while we state for the user to modified the readme file, we don't tell them specifically to load/edit the `README.ex` file, nor do we tell them to change the extension from `.ex` to `.md` after. I have made note of this. In the `Make some metadata.yaml` section, I removed the single quote from idempotent and changed the single quote in restart to a backtick so it stands out more.  Also changed the bootstrapped environment reference to point to the Getting Started page.