Reduced height of iframe.

Seeting the iframe height to 98% instead of 100% seems to be needed to
keep Chrome's PDF utility window from being cut off at the bottom of
the page.  This is at least on OSX with Chrome 39.0.2171.71 (64-bit).
Split out CSS for the main page into a separate file.
Firefox fix + modularization improvement.

1. I think I worked around the problems with Firefox. Previously, the
code that reloaded the PDF would actually get an error on Firefox and
fail to work entirely.  The new code does work in my environment on
OSX, though there are probably more elegant solutions than what I did.

2. Pulled out the CSS code and started a separate for it.

3. Came up with a name for this system: Vireo, for "VIewer for
REfreshed Output".
Fixed bugs in enableCheck().

1. If the current state is the new state given as the argument to
enableCheck(), don't do anything.

2. if we're enabling checks, a recomputation of the crc values
shouldn't be caused at the time enableCheck() is called because the
value it gets may be wrong because of the time when it's usually
called.  It's usually called in the same function that issued a reload
to the file, and it's apparently possible for the data to be either
incomplete or wrong or *something*.  It's better not to reload during
that time, and instead let a cycle pass.
No change -- just testing browser fixes.
No change -- more testing.
No change -- more testing.
No change -- more testing.
No change -- more testing.
Woops, turns out that \vfill doesn't help.
Reworked the front end.
Argh. Copied a test version and forgot to change file names.
Wrong file name!
Testing.
More efficient scheme allows us to increase the check frequency.

The code in crc-check.js and the back-end handler now provide an MD5
hash, so that the checker can transfer that each time instead of the
whole file every time.  This means a lot less data is being passed back
and forth, which means we can afford to increase the check frequency.
Use an md5 file on the server, CRC only as a fallback.

This now tries to download an MD5 has file from the server 1st, so that
the checker can transfer that each time instead of the whole file every
time.  This means a lot less data is being passed back and forth, which
means we can afford to increase the check frequency.
Testing.
Testing.
Images for the readme file.
Started a readme file to explain how to use all this.