corrected path to `CNeditor.css` referenced in comment.

Does this mean I should be editing `CNeditor.css` instead of the .styl
files here?
larger base font sizes, adjusted for display size.

[Matthew But­t­er­ick](http://practicaltypography.com/point-size.html),
author of Practical Typography, observes that a lot of people make the
body text too large in their print documents, but too small on the web.
A comfortable font size on the web is a little bigger than a
comfortable font size in print.
changed fonts and sizes to be relative to <body> element

It's much, much simpler, and also more in keeping with the principles
of "responsive design," set the font family and size once, and then
have all other elements inherit or adjust from this default setting. So
I deleted repeat references to the font family wherever they were the
same as the default. And for the body element, which adjusts somewhat
based on media queries, I changed font size units to em.
Rethinking how much styles scale font-size up or down.
shorter line lengths for note area; adjusted position of #note-file-list

Most typographers recommend line lengths between 45 and 90 characters,
or between 2 and 3 *alphabets*. This commit sets #note-style to a max-
width of 40em, which works out almost exactly to 3 alphabets at the
widest. So it's still on the wider end of that recommended range. But
because the text is narrower now, users won't have to jump so far when
they move their eyes across the page as they read.

This necessitated adjusting the position of #note-file-list to maintain
the look of a paperclip attached to the notes page. However, it's
possible that the file list could also look good if it were floated to
the right of the note area, forming a third column for sufficiently
large client displays. Maybe?
converted most CSS lengths to *relative* units.

Using relative units (like em and percentages) instead of absolute
units (like pixels and inches) is central to "responsive design." I
think, if you can help it, usually the only element that needs fixed
units should be the <body> font-size, and that should probably be
adjusted based on display size using media queries. Another exception
would be bitmap graphics, which don't scale as well. CSS lengths based
on em will scale with the font size for different display devices, or
scale with user browser stylesheets which change the default font size.
And percentages will scale with the device display size.

So that's what I've done here.

Lengths of '0' are the same regardless of the unit, but in those cases
I removed 'px' anyway because it might encourage other contributors to
keep the pixel unit if they change that particular CSS property, which
generally I don't think we want.

...By the way, what does the #drag style, in `note.styl`, apply to? I
didn't change the lengths there to relative units because I couldn't
figure out what it was; I could not make this element id appear
anywhere in the markup in my test Cozy Notes app.

I also did *not* edit the "Datepicker for Bootstrap" styles in
`CNeditor.css`, though it was a little hard to tell where exactly the
Bootstrap styles ended... If those styles are from Bootstrap, I figured
you'd want to keep them the same as the upstream version. Right?

I'd like if the .Th, .To, .Th, .Lh, .Lo, and .Lu styles -- the notes
bullet points -- were indented a little more, but there would need to
be fewer indentation levels, or else the largest indents would be wider
than the #note-style container.
minor change, after noticing the #nav block has *inline* styles.

Before, the margin styles here were a little contradictory, since
'margin:' set the left and right margins to 0, but then 'margin-left'
and 'margin-right' set them to percentages...

What I really wanted to do next here was use a media query to change
the positioning of the #nav block for smaller displays, so that smaller
devices would get a single-column layout, saving precious screen space
when actually editing their notes. However, the #nav position is set
inline, so I can't make any changes from the stylesheet.
fixed overlaps in breadcrumb and file list at small display sizes.
Element positions should generally be set by stylesheets not hard-coded inline style attributes.
Made #note-file-list and breadcrumb styles simpler, more consistent.
Added Source Sans Pro font files, and adjusted fonts in stylesheets.

As I noted in comments at the top of `base.styl`, the TrueType Font
file was taken from the Google Fonts repository, and converted to other
font formats using the Font Squirrel web service. Using this method
will require settings bold and italic styles using the `font-family`
CSS property instead of `font-weight` and `font-style` properties.
Otherwise web browsers approximate their own version of bold and
italic, instead of using the actual bold and italic font faces.
Merge pull request #42 from Terrycloth/responsive-design

First steps toward a responsively designed client