`flag_f_vector` for polyhedra

[gh-kliem]

We add a method to Polyhedron_base and CombinatorialPolyhedron, which wraps flag_f_polynomial of FiniteLatticePoset so that flag_f_vector(1,3) returns the f_{1,3}.

[gh-kliem]

New commits:

​d3d4285	tempory commit
​aefbc44	flag_f_vector for combinatorial polyhedron
​fe7d4bb	flag-f-vector for Polyhedron_base

[jipilab]

A few things:

• In the documentation, (number of faces of each dimension) should not say the same as the f-vector but say what the flag f-vector counts.
• Remove the backticks and add dash (in combinatorial polyhedron too):

  -        Return the `flag_f_vector`.
  +        Return the flag f-vector.
  

  -        For each `-1 < i_0 < \dots < i_n < d` the `flag_f_vector`
  +        For each `-1 < i_0 < \dots < i_n < d` the flag f-vector
  

• Backticks missing here (in combinatorial polyhedron file too):

  -        counts the number of flags `F_0 \subset \dots \subset F_n
  +        counts the number of flags `F_0 \subset \dots \subset F_n`
  

• Spelling (in combinatorial polyhedron too):

  -        - a dictionary, if no arguments where given
  -
  -        - an Integer, if arguments where given
  +        - a dictionary, if no arguments were given
  +
  +        - an Integer, if arguments were given
  

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​83709e2

typos

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​075c7a8

fixed index error

[jipilab]

Thanks! It looks good to me now.