Princurve

* MINOR CHANGES: Change all `T` to `TRUE`.

* MINOR CHANGE `plot.principal.curve()`: Rename argument `object` to `x`.

* MINOR CHANGE `lines.principal.curve()`: Rename argument `object` to `x`.

* MINOR CHANGE `points.principal.curve()`: Rename argument `object` to `x`.

* MINOR CHANGE: Rename internal function`start.circle()` to `startCircle()`.

* DESCRIPTION: Added Title and Maintainer field.

* MINOR CHANGES: Changed `F` to `FALSE`.

* DOCUMENTATION: Added keywords to `get.lam()`.

* DOCUMENTATION: Expanded documentation of `principal.curve()`:
added default values to usage, description, keywords and aliases.

* MINOR CHANGES: Changed precision in `getlam.f` from `v(2,10)` to `v(2,p)`.