bitflag_options-macrorules_v1: macro_rules impl of bitflag_options-v1

- generates same code as bitflag_options-v1 but implemented via macro_rules.
- slightly different call syntax due to macro_rules syntax constraints
  (notably: colon after Ident are not allowed)

bitflag-v3: simplification, fixes, improvements

 - simpl.: remove ConstrainedFlag wrapper. Merged its `bits` method in the
   Bitflag trait.
 - fix: fix parsing of macro to properly handle path expression as values
 - improvement: added try_punct to be able to handle punct like other
   try_ methods for macros
 - improvement: documented some macro functions
 - improvements: added hrtimer_mode example

bitflag-v2: factorisation and new bitflag module

This version the following changes were made:
 - creation of a bitflag module where Valid<Part> and Missing<Part> were
   moved and shared instead of being reimplemented by the macro every
   time
 - new BitFlag trait to characterise the bit type of a flag
 - new generic ConstrainedFlag<T:BitFlag>(T::bits) wrapper to
   replace the custom wrapper previously implemented by the macro. Now
   this custom type is a unit-like struct used to specify the
   ConstrainedFlag.
   This will allow shared trait implementations for multiple flags
   sharing bits types.
 - moved the builder() method to ConstrainedFlag
 - made the builder's build() method part of a documented trait in the
   module to publicise the common interface of all builders.

First draft of bitflag macro.

For a set of flags with combination constraints, this macro allows to
generate a Rust wrapper and its builder.

bitflag_options-v1: first draft of bitflag_options macro.

Define a fs::OpenOption-like named wrapper with a set of options as bool
functions wich set different user defined bitflags depending on the bool
value.