feat: Consistent and sensible layout_config (#922)

* feat: Consistent and sensible layout_config

* [docgen] Update doc/telescope.txt
skip-checks: true

* [WIP]: Thu 17 Jun 2021 03:36:44 PM EDT

* [WIP]: Thu 17 Jun 2021 03:38:11 PM EDT

* layout_default -> layout_defaults

* remove options from bug repot

* Conni2461 suggestions: part 1

* [docgen] Update doc/telescope.txt
skip-checks: true

* Conni2461 suggestions: part 2

* [docgen] Update doc/telescope.txt
skip-checks: true

* Linting

* Improve deprecation checks

- Move `layout_defaults` handling to `deprecated.lua`
- Check for "layout keys" outside of `layout_config` on `setup`

* fixup: Just add a few more words

Co-authored-by: Luke Kershaw <35707277+l-kershaw@users.noreply.github.com>
Co-authored-by: Github Actions <actions@github>

lua/telescope/builtin/init.lua

@@ -37,7 +37,7 @@
 ---       mappings = {
 ---         i = {
 ---           ["<c-d>"] = require("telescope.actions").delete_buffer,
----           -- or right hand side can also be a the name of the action as string
+---           -- or right hand side can also be the name of the action as string
 ---           ["<c-d>"] = "delete_buffer",
 ---         },
 ---         n = {