Move tests into `test` submodule.
Rename and reorg.
Change completion message.

Make it clearer it's showing the finish time (absolute clock time),
not the duration.
Command line flag changes:

1. Add `-s/--serve` command line flag.

`-s/--serve` runs the server, only (whereas `-p/--preview` runs the
server and also launches an external web browser).

The intended use of --serve is if you're running Frog remotely via
ssh, in which case to do a preview the web server needs to be there
but the browser would run on your local machine. Plus, the remote
server OS might not _have_ a GUI web browser --- or even if it does,
it would be silly to VNC to it when you could, um, use a web browser.

[Although I suppose you _could_ use --serve as the production server
for a blog, that's _not_ the intent. The intended use is just for
preview, and you will deploy the files to some other static web server
that's the real, production server.]

2. `-w/--watch` is now a modifier flag that must be specified in
addition to, and before, either `--serve` or `--preview`.

(Previously it meant watch-and-preview, by itself.)

3. Some flags may now be specified multiple times. Examples:

    # Create a couple markdown post source files:
    raco frog --new "Post 1" --new "Post 2"

    # Build, then preview with watch, then a final build
    # (because --watch currently doesn't guarantee a full build):
    raco frog --build --watch --preview --build
Supply `#:listen-ip #f` to `serve/servlet`.

Allows --serve to work with remote connections, which is the intended
use case for previous commit 4e61b1e.
Add `--ns` commaand line flag. This works just like `-n`, but it
creates a .scrbl file, instead.
Add drop<=
Handle case of 0 blog posts. Fixes issue #52.
Fix commit 0c52c125: Use `directory-exists?` not `file-exists?`.
Merge pull request #51 from ebzzry/master

Add ability to generate Scribble format post files, too.
Merge branch 'master' of github.com:greghendershott/frog

* 'master' of github.com:greghendershott/frog:
  Add `--ns` commaand line flag. This works just like `-n`, but it creates a .scrbl file, instead.
A few small revisions to commit 191301e0

- Don't use Markdown italic style in the Scribble post template.

- Tweak some command line flags to fit my admittedly subjective
  preference.
Improve meta-data match. Fixes #53.

Specifically, be prepared for an x-expression value that is not simply
one string.
_ not else in match
More permissive <!-- more --> jump markers.
README: Note raco setup bug in Racket HEAD
Update README re building Racket from HEAD.

Mention the commit that fixed the issue with `raco pkg install frog`.
Use find-parent-dir to find .frogrc

Untested because I cannot figure out how to install find-parent-dir.
deps: Use the short form "find-parent-dir"

... since apparently samth already registered the package at
https://pkg.racket-lang.org/info/find-parent-dir
Use the "only-in" form of "require", for explicitness