Support stroke patterns (i.e. dashed/dotted lines).

Support stroke patterns (i.e. dashed/dotted lines).

Patterns can be arbitrarily complicated sequences of lines and breaks,
or pre-built constants like Dygraph.DOTTED_LINE.

See tests/per-series.html for an example of how this works.

commit 214caf668bb8472605c505c124fd14e5d3b5a956
Merge: db2e28c 25c4046
Author: Dan Vanderkam <danvk@google.com>
Date:   Thu Jan 26 17:33:08 2012 -0500

    Merge branch 'stroke_pattern' of https://github.com/bluthen/dygraphs into bluthen

commit 25c40460bbd25f05cfd0be9da3535dd4662cfadb
Author: Russell Valentine <russ@coldstonelabs.org>
Date:   Thu Jan 26 14:43:14 2012 -0600

    Few changes suggested by Dan Vanderkam.

commit a9965f34b5470c2db5656cac1d8d3debd3a0d4e7
Author: Russell Valentine <russ@coldstonelabs.org>
Date:   Thu Jan 26 00:41:44 2012 -0600

    Stroke patterns in the legend that scale to 1em.

commit 62f2905c52e6936339dd1de7af1844aaced95c05
Author: Russell Valentine <russ@coldstonelabs.org>
Date:   Sat Jan 21 12:14:03 2012 -0600

    Sets dimensions for graph div in dash test so it could pass if default size ever changes.

commit bfece39cc4f2e365cf692b81cffdf91a773625ac
Author: Russell Valentine <russ@coldstonelabs.org>
Date:   Fri Jan 20 17:22:33 2012 -0600

    Added a simple dash unit test. It tests if it draw the correct number of lines
    and remembers pattern history between points.

commit 57539c89e29a1e45a6d1000ebe53c496eb88a61b
Author: Russell Valentine <russ@coldstonelabs.org>
Date:   Wed Jan 18 23:50:13 2012 -0600

    Comment wording changes. Added default string stroke patterns object to allow for more code reuse.

commit de286626b93dc7ce49ce50abfba83ffaa29db068
Author: Russell Valentine <russ@coldstonelabs.org>
Date:   Wed Jan 18 22:48:16 2012 -0600

    Use "font-weight: bold"  in style instead of the bold tag.

commit f5958230321df474bfb1339b9a97c64f92f20621
Author: Russell Valentine <russ@coldstonelabs.org>
Date:   Wed Jan 18 22:12:50 2012 -0600

    Reverted CanvasAssertions.js to have no modifications.
    Moved array compare function to dygraph-utils.
    Moved dashedLine into DygraphCanvasRenderer instead of in
    CanvasRenderingContext2D. Added some comments and used better variable
    names. Included are some lint warning fixes and style conformity changes.

commit 4b5e255dff699f59a5ced5186c4e4558b09a4003
Author: Russell Valentine <russ@coldstonelabs.org>
Date:   Wed Jan 18 14:33:13 2012 -0600

    Actual dashedLine coordinates checked now. Oops.

commit a5930c675465e6566854d3b6e2b9d6fa606ce91c
Author: Russell Valentine <russ@coldstonelabs.org>
Date:   Wed Jan 18 14:25:51 2012 -0600

    per series stroke pattern support.