Improved documentation

Extended documentation for bind() and return value from eval().
Merge pull request #4 from njohnston/docs.

Improved documentation
Clarify a few things
fix for old v8
Convert js objects to perl blessed references

Corresponding perl packages are created and filled with methods from
object prototype.
Convert perl objects to js

Object prototype is created and filled with methods from
perl package that object is blessed into.
Revert "Convert perl objects to js"

This reverts commit 578b817d2f312079330c36ef66694cb261d11f73.
Convert perl objects to js

Object prototype is created and filled with methods from
perl package that object is blessed into.
Extract get_prototype() for clarity.
Use Object::SetHiddenField() to store perl object pointer.
Added methods allowing to force v8 gc
Fix converted perl objects leaks
Blessing JavaScript object conversion is now optional.

Introduced enable_blessing and bless_prefix options to
JavaScript::V8::Context::new().
Merge branch 'plobj'
Allow custom V8 build dir to be specified with V8_DIR environment var.
Added set_flags_from_string() binding for V8::SetFlagsFromString().
Use --expose-gc to force gc in recent v8 versions.
Memoize already converted objects.

Speed up conversion and properly handle circular data structures
by caching all seen arrays and objects.
Removed implemented items.
Include filename and line number into error messages