to do list

* Separate arrows, possibility to add them to curves.

* Conversion pt -> bp will omit the scale factor at the output. (multiplying
the dimension by 0.99626401 before removing pt).

* Add operator for rotation. (Otherwise graphics should be used.)

*? Test slope coordinates to be real number (see below), not rounded to zero.
Ths is pribably not necessary - too complicated, waste of computer time and
with almost no interesting effect.

\def\pIIe@tilldot #1.{#1}
\def\pIIe@RealToParts #1.#2:#3#4{%
  \def #3{#1}%
  \ifx #3\empty \edef #3{0}\else \ifx #3\space \edef #3{0}\fi\fi
  \def #4{#2}
  \ifx #4\empty
    \def#4{0}%
  \else
    \edef #4{.\expandafter\pIIe@tilldot #4}%
  \fi}
\newcommand*\pIIe@checkslopeargs[2]{%
  \pIIe@checkslopearg{#1}%
  \pIIe@checkslopearg{#2}%
  \ifdim #1\p@=\z@ \ifdim #2\p@=\z@ \@badlinearg \fi \fi}
\newcommand*\pIIe@checkslopearg[1]{%
  \def\@tempa{#1}\expandafter\pIIe@RealToParts\@tempa.:\@tempb\@tempc
  \ifnum\@tempb<\z@ \edef\@tempb{-\@tempb}\fi
  \ifnum \@tempb>16383
    \@badlinearg
  \else
    \ifnum \@tempb=16383 \ifdim \@tempc\p@>.99998\p@ \@badlinearg \fi \fi
  \fi}
\newcommand*\pIIe@checkslopeargsvector[2]{%
  \pIIe@checkslopeargs{#1}{#2}%
  \@tempdima #1\p@ \ifdim \@tempdima>1000\p@ \@badlinearg \fi
  \@tempdima #2\p@ \ifdim \@tempdima>1000\p@ \@badlinearg \fi}
\def\@badlinearg{\PackageError
  {pict2e}{Bad \protect\line\space or \protect\vector\space argument}{}}