New feature: Granular rebuilds

The `rebuild` command is now much more powerful. You
can still these things:

```
rebuild file.mdsh > file.html
rebuild file.md   > file.html
```

...and so on.. But now you can do much more "granular"
rebuilds, where only specific pages are rebuilt.

Here are the new commands:

```
rebuild homepage            # rebuild index.html (the homepage)

rebuild archive             # rebuild archive.html

rebuild 404                 # rebuild 404.html

rebuild search              # rebuild search.html

rebuild authors             # rebuild all pages in authors/

rebuild authors:foo,bar     # rebuild pages authors/foo.html and tags/bar.html

rebuild categories          # rebuild all pages in categories/

rebuild categories:foo,bar  # rebuild pages categories/foo.html and tags/bar.html

rebuild tags                # rebuild all pages in tags/

rebuild tags:foo,bar        # rebuild pages tags/foo.html and tags/bar.html

rebuild years               # rebuild all posts/<years>/index.html index pages

rebuild years:foo           # rebuild posts/foo/index.html specifically

rebuild months 2019         # rebuild all monthly index pages in posts/2019/

rebuild months:foo 2019     # rebuild posts/2019/foo/index.html specifically
```

You can also combine them like so:

```
rebuild authors:bob tags:foo,bar 404
```

.app/cli-interface.bash

@@ -53,10 +53,6 @@ function rebuild {
     ${PWD}/.app/create_page.sh $1 $2
     return 0
   fi
-  if [ "$1" = "homepage" ];then
-    post_title="Homepage" ${PWD}/.app/create_page.sh > index.html
-    return 0
-  fi
   if [ "$1" = "rss" ];then
     .app/create_rss.sh posts/ > feed.rss
     return 0
@@ -65,8 +61,8 @@ function rebuild {
     ${PWD}/.app/generate_sitemap.sh
     return 0
   fi
-  # $1 might be a parameter, like -all
-  ${PWD}/.app/update_pages.sh $1
+  # $1 might be a parameter, like 'tags', 'year:2019', 'authors:foo,bar', '-all', ...
+  ${PWD}/.app/update_pages.sh $@
 }
 
 function help {