Move from spritesmith to postcss-sprites.

[ilyoff]

I suggest to move from spritesmith to postcss-sprites:

• There is the same spritesmith module under the hood, so the quality of sprites will not changed
• It has useful filterBy and groupBy options, which makes him very flexible
• Out of the box makes sprites by retina prefixes (@2x, @3x, @4x), which resolves #321, and also makes prefixes customizable
• We can get rid from sprite mixins by automatically adding needed rules to css file with onupdaterule hook or with separate plugin. That will help to resolve #314, cause will work without any non-standard css functionality (ex. postcss-mixins)
• Also duplicates problem, mentioned in #257, when there are two images with the same name, but located in different directories, resolved by adding both images to the sprite, cause they are still different by location, which is right case, IMHO.

If this is ok, I can implement it

[artem-malko]

Cool! As I understand raster-sprite for ie8 will not work with that approach, will it? I mean raster sprite of raster svg-icons.

[ilyoff]

I think, we can deal somehow with it, but at last, can't we drop ie8 support in the end of 2018?)

[artem-malko]

Ok, let's drop ie8. Add a warning message, if build was started with ie8 support. We need to make it mush more obviously for that users.

[DaveDev13]

Есть ли вообще смысл дальнейшей поддержки IE8? На сколько понимаю из плюх для неё остаётся лишь сборка отдельного файла стилей

[ilyoff]

@artem-malko you mean something like "ie8 no more supported?"

[artem-malko]

@CcRaZyY и js) shim-файлы. @ilyoff 👍 Only for sprite generation. css and js have to be processed correctly. We can drop IE8 full support later.

[artem-malko]

@ilyoff up) Will you develop with issue?)

[ilyoff]

@artem-malko hi, yeah, half work already done) Sorry for taking this so long

[artem-malko]

@ilyoff it's ok) Just sync info, I do not hurry you)