all: assorted cleanups and updates

Changes include:
  - add a bunch of "noexcept", mostly to operators and forceinline
  - use "uchar"
  - use "charptr"
  - rename options_t to Options
  - add ptr_check_no_overlap()
  - rewrite p_exe.cpp, NFCI
  - clang-format help.cpp
  - spelling fixes

doc/upx-doc.html

@@ -160,7 +160,7 @@ Copyright (c) 1996-2023 Markus Oberhumer, Laszlo Molnar & John Reiser
 
 <p>Info: An &quot;overlay&quot; means auxiliary data attached after the logical end of an executable, and it often contains application specific data (this is a common practice to avoid an extra data file, though it would be better to use resource sections).</p>
 
-<p><b>UPX</b> handles overlays like many other executable packers do: it simply copies the overlay after the compressed image. This works with some files, but doesn&#39;t work with others, depending on how an application actually accesses this overlayed data.</p>
+<p><b>UPX</b> handles overlays like many other executable packers do: it simply copies the overlay after the compressed image. This works with some files, but doesn&#39;t work with others, depending on how an application actually accesses this overlaid data.</p>
 
 <pre><code>--overlay=copy    Copy any extra data attached to the file. [DEFAULT]
 

doc/upx-doc.txt

@@ -153,7 +153,7 @@ OVERLAY HANDLING OPTIONS
     UPX handles overlays like many other executable packers do: it simply
     copies the overlay after the compressed image. This works with some
     files, but doesn't work with others, depending on how an application
-    actually accesses this overlayed data.
+    actually accesses this overlaid data.
 
       --overlay=copy    Copy any extra data attached to the file. [DEFAULT]
 

doc/upx.1

@@ -296,7 +296,7 @@ it would be better to use resource sections).
 \&\fB\s-1UPX\s0\fR handles overlays like many other executable packers do: it simply
 copies the overlay after the compressed image. This works with some
 files, but doesn't work with others, depending on how an application
-actually accesses this overlayed data.
+actually accesses this overlaid data.
 .PP
 .Vb 1
 \&  \-\-overlay=copy    Copy any extra data attached to the file. [DEFAULT]

doc/upx.pod

@@ -208,7 +208,7 @@ it would be better to use resource sections).
 B<UPX> handles overlays like many other executable packers do: it simply
 copies the overlay after the compressed image. This works with some
 files, but doesn't work with others, depending on how an application
-actually accesses this overlayed data.
+actually accesses this overlaid data.
 
   --overlay=copy    Copy any extra data attached to the file. [DEFAULT]