Move the computed style to a new SharedLayoutData struct.

Implementing the CSSOM requires giving the script task access to the
computed style for a node. Moving it into a new SharedLayoutData struct
member of LayoutDataRef seems to be the best way to achieve this.

This is the first step towards #1721.
Remove the argcAndIndex argument from instantiateJSToNativeConversionTemplate.

This commit does not change the generated code.
Remove the isOptional argument and the dealWithOptional return value from getJSToNativeConversionTemplate.

Note that dictionaries currently don't support members without default values
right now.

This commit does not change the generated code.
Rename GlyphIndex->GlyphId

This will allow us to use the GlyphIndex identifier to refer to glyph indexes into text runs in the future.
Add RangeIndex trait and iterator

This will allow for the definition of typesafe range units in the future, for example for glyph indices. This also adds a macro that allows for the easy implementation of new range index types.
Add some trailing commas
auto merge of #2388 : zwarich/servo/cssom, r=jdm

Implementing the CSSOM requires giving the script task access to the
computed style for a node. Moving it into a new SharedLayoutData struct
member of LayoutDataRef seems to be the best way to achieve this.

This is the first step towards #1721.
Add character index type

This is more self-documenting and may highlight errors in the future.
Add some helpful comments
Use box index type for referring to inline boxes
Fix file mode for servo.rs

For some reason this was set to +x
Handle all attributes coming from the HTML parser (fixes #1976).
auto merge of #2414 : Ms2ger/servo/parser-attribute, r=SimonSapin
Reuse Constellation::find_all in Constellation::handle_load_iframe_url_msg.
Use a match rather than a for loop for last_loaded_url in ScriptTask::load.
Merge Page and PageTree.
auto merge of #2415 : Ms2ger/servo/find-all, r=jdm

...sg.
fixup! Use a match rather than a for loop for last_loaded_url in ScriptTask::load.
Use fragment index type for referring to inline DOM fragments
auto merge of #2389 : bjz/servo/indices, r=pcwalton

r? @pcwalton