rename identifiers to be prefixed by smartcan

renamed to create the pseudo-namespace as promoted by MELPA maintainers
fix comments by prefixing smartscan where appropriate
turn smartscan into global minor mode with keymap
add installation comments
add installation comments to README.md
Fix typo
Add contributions
Rename smart-selector to smartscan-symbol-selector
Rename minor mode smartscan to smartscan-mode to conform with Emacs convention.
Update docstring for smartscan-mode to explain what it does.