Clarify LibEx directory on Windows

[SteveLasker]

The directory structure spec calls out LibEx files to be placed in the root of %ProgramFiles%. Windows uses nested folders to isolate binaries and config specific to each executable. This includes configuration as well.

This spec seems to call ou BIN is under a subfolder, but LIBEXEC and CONFIG are not.

Directory	Unix	Windows	Darwin
BIN	/usr/bin	%ProgramFiles%/notation/bin	/usr/local/bin
LIBEXEC	/usr/libexec	%ProgramFiles%	/usr/local/lib
CONFIG	/etc	%ProgramData%	/Library/Application Support

This issue clarifies that all notation components should be under a sub-directory on Windows, not just the BIN.

Suggesting the following:

Directory	Unix	Windows	Darwin
BIN	/usr/bin	%ProgramFiles%/notation/bin	/usr/local/bin
LIBEXEC	/usr/libexec	%ProgramFiles%/notation/bin	/usr/local/lib
CONFIG	/etc	%ProgramData%/notation/	/Library/Application Support

The Windows examples section seems to imply these are sub directories, so it looks like the above just needs a bit more consistency across platforms as each platform stores notation in a sub-directory.