add --rename option to rename declarations and references

The `--rename` option takes a string as input, treating every couple, separated by a space,
as a find-replace option.
For example,  `--rename "$theService $myService "theFactory myFactory"` will replace `$theService` with `$myService` and `theFactory` with `myFactory` in both the declaration and in any annotation that will be added by ng-annotate. The actual use of the provider won't be changed.

Closes #44
Most of added "let"s should be replaced with "const"s. Even this one ("const" is shallow constant, you can still mess with keys).