introduced RenderWithOptions method, changed RenderTo signature; modi…

[whisk]

Draft for RenderWithOptions method, refers to #96

[whisk]

As I made some changes in styles package to ensure that CssNode implements Node, that led to changes in styles_test.go to remove circular dependencies.
Any ideas on how to improve that?

[chasefleming]

The main package should probably be tested independently without the dependency on subpackages -- since they are optional -- so I think TextNode is fine. Could make the argument that the tests in the elem package should also remove the use of attrs subpackage (e.g. use plains string instead of the attrs constants). We should probably add a test for CSSNode then though in the styles package.

[chasefleming]

Can you add this comment above this line please? // DisablePreamble disables the doctype preamble for the HTML tag if it exists in the rendering tree.

[chasefleming]

Also, since these options actually are present on any element calling Render what do you think about being more specific with a name like DisableHtmlPreamble, DisableDocumentPreamble, or DisableDocPreamble?

[whisk]

DisableHtmlPreamble looks pretty self-explanatory, as we call it for html tag. Also added the comment.

[chasefleming]

Looks good, thanks!