New unified directory structure

[vrza]

This is to simplify supporting both developer/portable installation and system-wide installation with default config. New structure is:

# binary
${PREFIX}/bin/123
# runtime files
${PREFIX}/share/lotus/123.v10
# keymaps
${PREFIX}/share/lotus/keymaps
# default config
${PREFIX}/share/lotus/etc/l123set.cf

Where ${PREFIX} can be developer's project directory 123elf, or /usr, or /usr/local, or /opt/lotus etc.

Replaces the following PRs:

• Cleaner extract script Cleaner and more verbose extract.sh; drop bash dependency #67
• Search for runtime files in shared directory Search for runtime files in shared directory, to support system-wide installation #68

Will simplify implementation of:

• make install target adds install target #20

Also should fix the issue with slow file seek onWSL2.

[taviso]

Thanks for the rebase, merged with these changes:

• I don't want to drop the .sh extension, I find it a useful clue what's in there!
• I added a convenience symlink to the main binary.
• I moved the keymaps, so extract doesn't have to touch them anymore.
• Added the new directories to gitignore.

It seems to work okay, looks much neater for eventual packaging!

[vrza]

@taviso Thanks! A couple of remarks:

• no need to remove root/, was replaced by share/
• just like with binutils.sh and gzip.sh we can call ./extract.sh clean from the distclean target, it will remove stuff created by that script

Now that the foundation is in place I'll look into creating an install target and then we're ready for packaging!

[taviso]

Good points, fixed!