Transfer of old work
Split "Search project code.do" into parameters.do search.do.
Added parameter `extensions'.

The user can now search specified additional file extensions.
Added parameters `stata' `help' `mata'.

The user now has detailed control over which file extensions are
searched.
Moved code within the search section.
Added regular expression tips.
Modified the comments at the top.
Added .gitignore file.
Modified the `regex' tips.
Command line use supports new parameters.
Slight tweak: reordered the list of binary parameters.
search.do is run quietly.
`dirs' accepts system directory codes.