orbitr 0.2.0

New functions

add_body_keplerian(): Add a body to the system using classical Keplerian orbital elements (semi-major axis, eccentricity, inclination, longitude of ascending node, argument of periapsis, true anomaly) instead of raw Cartesian state vectors. The elements are converted to position and velocity relative to a specified parent body.
add_planet(): Add a known solar system body by name with real orbital data looked up automatically. Just specify the name and parent — mass, semi-major axis, eccentricity, inclination, and orientation are filled in from JPL DE440 values. Any element can be overridden for “what if” scenarios (e.g., add_planet("Mars", parent = "Sun", e = 0) for a circular Mars).
load_solar_system(): One-liner that builds a complete solar system — the Sun, all eight planets, the Moon, and optionally Pluto — using real orbital data from the JPL DE440 ephemeris. Returns a ready-to-simulate orbit_system. Use moon = FALSE or pluto = FALSE to exclude those bodies.

three_d parameter on plot_orbits(), plot_system(), and animate_system() now supports FALSE to force 2D output even when the data has Z-axis motion. Previously, three_d = FALSE was the default but could not override the auto-detection.
Fixed frozen 3D animations in animate_system_3d() caused by redraw = FALSE in plotly animation options.

Initial release.

N-body gravitational simulation with three integration methods: Velocity Verlet (default), Euler-Cromer, and standard Euler.
Compiled C++ acceleration engine via Rcpp with automatic fallback to vectorized R.
Optional gravitational softening to prevent singularities at close approach.

create_system() / add_body() / simulate_system() pipe-friendly API.
Tidy tibble output (one row per body per time step) for use with dplyr, ggplot2, plotly, etc.
shift_reference_frame() to re-center simulations on any body.

plot_orbits() / plot_orbits_3d() for quick trajectory plots (ggplot2 2D, plotly 3D).
plot_system() / plot_system_3d() for single-time-step snapshots.
animate_system() / animate_system_3d() for animated orbits via gganimate or plotly.
Automatic 2D/3D dispatch based on whether any body has non-zero Z motion.

Real-world masses, orbital distances, and speeds for the Sun, all eight planets, and the Moon.
gravitational_constant for scaling gravity in create_system().
seconds_per_hour, seconds_per_day, seconds_per_year time helpers.