update docs link

This commit implements the new transformation model, but it also
needs to modify a few tests to fit the new format. This is still
a work in progress.

This commit updates the README with up to date instructions about
how to run and build the library, as well as how to run the tests,
playgrounds and performance tests

convey our current published version clearly

* fix wrong doc for local testing

* fix html ending - thanks @RmiTtro

Fix command to build and added a small section about testing

The note for "Size and position" has been edited for consistency.

The category "Altering the element tree" has been renamed "Document tree manipulations".

The `transform()`, `rotate()`, `skew()`, `scale()`, and `translate()` methods have been given their own category: "Transforms".

The "Transforming elements" section has been renamed "Size and position".

The `transform()` method has been moved to the "Geometry" section.

The "Syntax sugar" section has been broken up and removed:
* `radius()` has been moved to "Size and position" (and has been edited for completeness and clarity)
* `fill()`, `stroke()`, and `opacity()` have been moved to "Attributes and styles"
* `rotate()`, `skew()`, `scale()`, and `translate()` have been grouped with `transform()` under "Geometry"

The 'Manipulating elements, 'Attribute references', and 'Inserting elements' sections of the documentation are reorganized. 'Manipulating elements' has been broken up into 4 sections:

* Attributes and styles
* Classes
* Transforming elements
* Altering the element tree

The 'Attribute references' section is folded into 'Attributes and styles', and the 'Inserting elements' section is folded into 'Altering the element tree'.

Some general information about positioning methods has been added/moved to a note at the beginning of the 'Transforming elements' section.

Many of the method descriptions in these sections have been edited for clarity, and a few typos have been fixed.