Add load_coord() and load_fields() to load HARM data
Load the data into device memory instead of host memory
Add three radiactive flux channels
Add a second viewport to display the image
Render the traced image with OpenGL shader

TODO: we should use glTexSubImage2D() for this feature but I'm not
awake to learn it now.
Take general relativistic effects into account
Merge branch 'develop' into harm

Conflicts:
	src/vis.cc
No need to store kt0 because k.u_obs = 1 initially
Obtain the ray traced image of a non-rotating torus
Fix bug: need sqrt(g00) in redshift because u.u=g_{\mu\nu}u^\mu u^\nu
Fix bug: use k_t instead of k^t in redshift, which is constant
Make the torus spin at angular velocity = 0.5
Merge branch 'harm' into develop

Create ray traced image of a torus without loading harm data.
Introduce two new parameters R_torus and Omega in "src/Kerr/para.h"
Set R_torus and Omega by 'R=...' and 'O=...', respectively
Reduce the number of floating point operations; update FLOP_RHS
Correct radiative transfer equation; use a physical Omega as default
Solve for the radiative transfer equation in three channels
Return negative source because we use negative affine parameter
Merge branch 'harm' into develop