fix(examples): fix binding of instance method/property

The :: descriptor didn't handle correctly the instance property.
A proxy was created each time, making the test of existence or
value failing.
feat(environment): itsInstance now support property access

Using itsInstance 'property', it's now possible to create a test
for the value of the property of a created instance.
feat(environment): withParamteters now support a context block

It's now possible to pass a block to the withParameters and withArguments
helper. In that case the block will be evaluated in the current context
and have to return an array.

BREAKING CHANGE: breaks specs that was passing a function as first argument

    A test that was using:

    withParameters -> 'a function passed as first argument'

    Will be transformed like this:

    withParameters -> [-> 'a function passed as first argument']
feat(examples): owner of an instance method is stored in context
fix(utils): circular references in utils.inspect

Circular references are now marked with [circular].
feat(environment): itsReturn now support with and inContext options

These options allow to specify the this object and arguments for
the subject call.
fix(matchers): fix call to valueOf on undefined value
style(environment): remove arguments and context of itsReturn description
refactor(Cakefile): avoid blob string for commands options
refactor(utils): move String::capitalize to utils

Native object extensions is now limited to Object and Function.
feat(utils): add utils.strip method

The strip method removes whitespaces at the beginning
and the end of a string.
feat(dom): first implementation of match and contained methods
feat(dom): implements node's text content matching

Includes:
  - using quotes the node's text must equal the passed-in string
  - using slashes the expression is used as a regexp and tested
    on the node content
  - add some basic format validation:
    * no indent on the root level
    * indent have 2 spaces
feat(dom): implements support for negative indent offset
refactor(dom): rename DOMParser as DOMExpression
feat(fixtures): implements dom fixture loading

Includes:
  - add support for dom files in the fixture method
  - add support for dom expressions in the match matcher
  - add a contains matcher that support dom expressions