rewrite: slimmer, trimmer and more lazy kickstart.nvim (#635)

We've removed over 1/3 of the code that was in kickstart previously,
and more than doubled the amount of comments explaining every line
of code (to the best of my ability).

kickstart now properly uses many of the lazy.nvim config and loading
idioms, which should be really helpful for people moving both to
modular configs, as well as extending the kickstart config in one file.

Additional features:
- Beautiful ascii art
- Added some documentation that explains what is an LSP, what is telescope, etc
- There is now a `:checkhealth` for kickstart, which checks some basic information
  and adds useful information for maintainers (for people cloning the repo).
- Improved LSP configuration and tool installation, for easier first time startup
- Changed init.lua ordering, so that it moves from simple options to complicated config

```
-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
Lua                              1            108            404            298
-------------------------------------------------------------------------------
```

1 files changed, 51 insertions, 0 deletions

diff --git a/lua/kickstart/health.lua b/lua/kickstart/health.lua
new file mode 100644
index 0000000..957204e
--- /dev/null
+++ b/lua/kickstart/health.lua
@@ -0,0 +1,51 @@
+--[[
+--
+-- This file is not required for your own configuration,
+-- but helps people determine if their system is setup correctly.
+--
+--]]
+
+local check_version = function()
+  if not vim.version.cmp then
+    vim.health.error(string.format("Neovim out of date: '%s'. Upgrade to latest stable or nightly", tostring(vim.version())))
+    return
+  end
+
+  if vim.version.cmp(vim.version(), { 0, 9, 4 }) >= 0 then
+    vim.health.ok(string.format("Neovim version is: '%s'", tostring(vim.version())))
+  else
+    vim.health.error(string.format("Neovim out of date: '%s'. Upgrade to latest stable or nightly", tostring(vim.version())))
+  end
+end
+
+local check_external_reqs = function()
+  -- Basic utils: `git`, `make`, `unzip`
+  for _, exe in ipairs { 'git', 'make', 'unzip', 'rg' } do
+    local is_executable = vim.fn.executable(exe) == 1
+    if is_executable then
+      vim.health.ok(string.format("Found executable: '%s'", exe))
+    else
+      vim.health.warn(string.format("Could not find executable: '%s'", exe))
+    end
+  end
+
+  return true
+end
+
+return {
+  check = function()
+    vim.health.start 'kickstart.nvim'
+
+    vim.health.info [[NOTE: Not every warning is a 'must-fix' in `:checkhealth`
+
+  Fix only warnings for plugins and languages you intend to use.
+    Mason will give warnings for languages that are not installed.
+    You do not need to install, unless you want to use those languages!]]
+
+    local uv = vim.uv or vim.loop
+    vim.health.info('System Information: ' .. vim.inspect(uv.os_uname()))
+
+    check_version()
+    check_external_reqs()
+  end,
+}