Add "Review Standards"

 * Simplify titles under "Common standards". (Use a noun-phrase instead of an imperative statement.)
 * Combine `r-ext`, `r-core` into r-technical. Add more details. Reference `#gotchas`.
 * Rename `r-read` to `r-code`
 * Rename `rg-schema` to `rg-upgrade`. Add more details.

Add warning about TRUNCATE TABLE to PHPUnit Tests doc.

standards/php.md - Add a TLDR example

To see actual examples of the coding style, you need to skim multiple blurbs
and click multiple links, and the eventual page shows very isolated
examples.

This revision adds a brief example so that a new contributor can get a
general sense of the layout immediately.

(Note: It's not possible for a brief example to show every edge-case, and we
shouldn't try -- that's why the commit also emphasizes the link into the
relevant examples from d.o docs.)

Add doc for WordPress shortcodes in extensions

typo

Asset builder example

ref:
https://github.com/civicrm/civicrm-wordpress/pull/112

Typo karama instead of karma

Port Content on Javascript Debugging from forum

Add in style guidelines on writing shell documentation as per isuse #…

Add warning not to use a space in username

GitLab doesn't allow spaces in the username.

Document extension dependencies in info.xml

Add in documentation on menu XML definition

Simplify language to make meaning clearer

Minor improvements to fix typos and style

This makes it easier to reference these things from other pages.

Broaden the "Coding Standards" chapter to "Development Standards" to
better encompass "Review Standards" as a page.