Updated guides with latest method [ci skip]

for blank?
fixed file name references [ci skip]
Updated guides with latest method [ci skip]
Removed doc of removed method diff [ci skip]
Fix the SQLite gem name
Add packages list for ArchLinux [ci skip]

Add the packages required on Arch Linux when setting up the development
dependencies
Revert "Fix the SQLite gem name"

This reverts commit 700c6c65bcce17d4c61423ceaef031bcbe203337.

Bot the `sqlite3` and `sqlite3-ruby` gems exist.
https://rubygems.org/gems/sqlite3
https://rubygems.org/gems/sqlite3-ruby

In fact, they both point to the same github repository.
https://github.com/luislavena/sqlite3-ruby

However, the last one hasn't been released since 2011, while the first
one keeps getting regular releases.
Refix my misreading of the diff

sorry @robin850.
Thanks @fxn
Add a SQL example for `not` [ci skip]

To share a certain logic across other examples, let's add a sample SQL
code generated by the given Ruby code
Use hyphenated version of assert_url [ci skip]
Fixes typo in Object#try!
Fix lixml2 to libxml2 [ci skip]
Using markdown-style code quotes
Typo fix
Merge branch 'master' of github.com:rails/docrails