Crate is converted to no_std

• Crate is converted into no_std
• Index and IndexMut are implemented
• prelude module is removed, required dependencies are added to lib
• Debug implementation is revised to only inform about the elements rather than impl details.
• Examples are added.
• Motivation section of the docs is revised.

PinnedVec version upgraded (3.3)

• PinnedVec and impelentors' versions are upgraded.
• Test coverage is improved.

PinnedVec version upgraded (2.11)

Merge pull request #27 from orxfun/PinnedVec-version-upgraded

PinnedVec version upgraded (2.11)

Improvements in the api

• Debug implementation is fixed, displaying the elements of the underlying pinned vector, rather than unsafe cell.
• PartialEq implementations are extended to all pinned vectors, standard vector and slice.
• FromIterator trait is implemented.
• with_ methods are added to create imp vectors with specific pinned vectors, such as with_doubling_growth or with_fixed_capacity.

IntoIterator is required for PinnedVec

• Upgraded the orx-pinned-vec dependency to version 2.9 which requires all pinned vectors to implement IntoIterator.
• IntoIterator is implemented for ImpVec.
• Tests extended.

Support for Concurrency: `zero_memory` argument in grow_to methods

Also UnsafeCell is made use of to model interior mutability.

`ImpVec` features are scoped and reduced

• ImpVec responsibilities are redefined / reduced:
  • ImpVec allows for imp_push and imp_extend_from_slice methods which enable growth with a shared reference.
  • It does not provide any methods to enable building self referential collections. Those features are formalized, structured and extracted to orx_selfref_col crate.
• documentation is revised accordingly.

Approach to build self referential collections is defined

The imp-vec approach to enable building self referential collections is more mature now through the following changes.

• The vector no longer needs and allows immutable push operation; instead it makes use of the push_get_ref and move_get_ref methods.
• Necessary unsafe methods are limited to a couple of methods and they are documented in detail.
• Safe methods which are useful in self referential collections are implemented:
  • replace_at
• self_referential_elements module is defined. In this module set_next and set_prev methods are defined for the elements implementing SelfRefNext and SelfRefPrev traits.
• FromIterator is implemented.
• Documentation revised.
• Code reorganized.
• Test coverage significantly increased.