Source Files / General Rules: limit line lengths to 80 columns

We currently say "stick with 80 if it's convenient, extend to 120
otherwise". This is too lax; much new edk2 code ignores the 80 columns
recommendation, resulting in source files that are hard to read for some
contributors. Remove the 120 columns excuse and make 80 columns a
requirement.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>

5_source_files/README.md

@@ -33,12 +33,19 @@
 
 ## 5.1 General Rules
 
-### 5.1.1 Lines shall be 120 columns, or less
+### 5.1.1 Lines shall be 80 columns, or less
 
-Preferably, limit line lengths to 80 columns or less. When this doesn't leave
-sufficient space for a good postfix style comment, extend the line to a total
-of 120 columns. Having some level of uniformity in the expected width of the
-source is useful for viewing and printing the code.
+Limit line lengths to 80 columns.
+
+Lines longer than 80 columns make it more difficult for the reader to find the
+beginning of the next line. They also tend to prevent users from displaying two
+source listings side-by-side on common display devices.
+
+When the 80 columns limit doesn't leave sufficient space for a postfix style
+comment, break the line into shorter segments at logical boundaries (for
+example, between the arguments of a function call, adhering to the spacing
+rules), or replace the postfix style comment with a standalone comment that
+precedes the statement.
 
 ### 5.1.2 Do not use tab characters
 

README.md

@@ -112,3 +112,4 @@ Copyright (c) 2006-2017, Intel Corporation. All rights reserved.
 | 2.1      | DRAFT for REFORMAT                                                                                                                                | 10/30/2015 |
 | 2.2      | Convert to Gitbook                                                                                                                                | June 2017  |
 |          | [#425](https://bugzilla.tianocore.org/show_bug.cgi?id=425) [CCS] clarify line breaking and indentation requirements for multi-line function calls |            |
+|          | Limit lines to 80 columns                                                                                                                         |            |