Copyright 2022 Matei Hriscu (311CA) <[email protected]>

For all commands, images are stored in the "img" struct which holds all image
attributes as well as a three dimensional array in which the pixels are stored,
regardless of the image type. img.matrix[i][j][k] refers to the kth subpixel of
the pixel on line i, column j. In the case of greyscale images there is only one
subpixel, while RGB images have 3.

In the main function, entire lines are read from stdin which are then split into
the command name and parameters. This way, there are never left overs left in
stdin after an invalid command or a command issued with the wrong number of
arguments.

LOAD:
The program will attempt to open the file that is specified as an argument and
if it is successful it will load the image into memory. If the operation fails
for any reason, the program will no longer have any image loaded.

SAVE:
The program will attempt to open the file that is specified as an argument and
if it is successful it will save the image by rounding all values to the nearest
integer.

SELECT:
Updates the image selection if the arguments are valid and retains the old
selection if they are not.

ROTATE:
Rotates the image by the provided angle if it is valid. The angle is first
reduced to the range [0, 360). 90 and 270 degree rotations are performed by
transposing and inverting the matrix at the same time while 180 degree rotations
are performed by just flipping the entire selection. 0 degree rotations are
skipped as they have no effect on the image.

CROP:
Creates a new image which only contains the current selection, then discards the
old image.

APPLY:
Firstly, a kernel matrix is created based on the filter name, then it is applied
to all pixels (except those near the edge where the aren't enough pixels to
perform the operation). The result is then clamped to ensure it stays between 0
and the maximum value of the image.

EXIT:
Frees all memory and gracefully exits the program.

In some of my header files you will find some pointers written as "foo * bar".
It was not my intention to write them this way, but writing them as "foo *bar"
incurs a coding style error.