This forces to use a copy when changes are needed. Internal mutable structures
have also been changed into immutable ones (i.e. lists have been turned into
tuples).
This change is a really useful first step to greatly optimize memory and time
needed to render large documents, as allows us to cache style dicts more
safely. It's been already done in StyleDict.inherit_from, with a ~5-10% memory
benefice.
Just as it's done in inline_min_content_width, the first_line attribute is now
used in inline_line_widths. It greatly improves performance for really long
texts.
Style is not copied anymore when boxes are duplicated. Style dicts are not
modified anymore during the layout, as it was before for some properties:
- margins, borders and paddings when the box was split between two
pages (useless as these computed values are stored directly in the box),
- top borders were changed in tables (useless for the same reason),
- bookmark labels and string sets are now stored in the box.
This commit can introduce very subtle bugs that are hard to debug. In the
future, we should try to freeze the style dicts before the layout.
Related to #70.
The hack had been added to remove extra line breaks caused by floating point
errors when the shrink-to-fit width was coming from Pango and had a slightly
higher value when re-calculated in split_first_line.
The same problem appears when we split a line contaning inline-blocks (instead
of letters in the previous case), as the shrink-to-fit width may also inderctly
come from Pango and hit the same re-calculation floating point errors.
This commit moves the hack at a higher level, increasing the max width before
calling split_first_line when the line contains letters (same result as
before), but also before splitting lines containing inline-blocks.
Fix#467.
