Replace uses of shorthand codeblock syntax to avoid issues with localization

Previously, many paragraphs in the documentation used `::` at the end of a line
as a replacement for a single colon (and `::` on the following line).
Due to this, the `::` was part of the extracted string for localization.
Weblate also showed a warning about the trailing `::`, as it's not
normally expected to be there.

This change requires translators to revalidate all modified strings.
However, considering many of those have broken code blocks due to translators
replacing `::` with `:`, it can be a good idea.

This also adds documentation writing guidelines for code blocks and admonitions.
This commit does not modify existing admonitions in any way (as this would
lead to a much larger diff, and require more localizable text to be revalidated
by translators).

tutorials/scripting/evaluating_expressions.rst

@@ -83,7 +83,9 @@ Passing variables to an expression
 
 You can pass variables to an expression. These variables will then
 become available in the expression's "context" and will be substituted when used
-in the expression::
+in the expression:
+
+::
 
     var expression = Expression.new()
     # Define the variable names first in the second parameter of `parse()`.
@@ -105,7 +107,9 @@ expression has no base instance associated to it.
 
 When calling :ref:`Expression.execute() <class_Expression_method_execute>`,
 you can set the value of the ``base_instance`` parameter to a specific object
-instance such as ``self``, another script instance or even a singleton::
+instance such as ``self``, another script instance or even a singleton:
+
+::
 
     func double(number):
         return number * 2
@@ -141,7 +145,9 @@ Associating a base instance allows doing the following:
 Example script
 --------------
 
-The script below demonstrates what the Expression class is capable of::
+The script below demonstrates what the Expression class is capable of:
+
+::
 
     const DAYS_IN_YEAR = 365
     var script_member_variable = 1000
@@ -191,7 +197,9 @@ The script below demonstrates what the Expression class is capable of::
         # The method's return value is also the expression's return value.
         return 0
 
-The output from the script will be::
+The output from the script will be:
+
+::
 
     false
     true