v0.9.0-rc1

BINDINGS/C++: Added explicit keyword
BINDINGS/C++: Added finish() to image_input and image_output
BINDINGS/C++: Added io_memory(arbitrary_data)
BINDINGS/C++: Added more constructors to io_memory
BINDINGS/C++: Added variant::clear()
BINDINGS/C++: Make image_output::next_frame() non-const
BINDINGS/C++: Refactor image_input
BINDINGS/C++: Refactor image_output
BINDINGS/C++: Update comments
BMP: Make marker constants as enum
CODECS: Remove I/O parameter from codec functions
CODECS: Remove parameters checks in codecs
COMMON: Make sail_bits_per_pixel() non-defensive
COMMON: Make sail_bytes_per_line() non-defensive
COMMON: Make sail_print_errno() non-defensive
COMMON: Make sail_string_hash() return 0 on empty input
COMMON: Remove orientation
COMMON: Rename 'flip' functions to 'mirror'
DOC: Added X10 X11 XBM specifications
EXAMPLES: Support CMake configurations that export SDL2::SDL2
LIBSAIL: Fix indent
LIBSAIL: Fixed allocating memory I/O for reading and writing when reading was not allowed
PCX: Added missing size of []
SAIL: Added SAIL_ENABLE_CODECS CMake option
SAIL: Remove extra quotes
SAIL: Rename junior functions to not have image in their names
SAIL: Rename loading/saving functions to have from/into in their names
TESTS: Added TGA images
TESTS: Added X11 XBM image
TESTS: Added XBM images
TESTS: Added more BMP files
TESTS: Detect codec info for loading from memory
TESTS: Move images to an upper level
TESTS: Rename PNG image
TGA: Note on avoiding mirroring
XBM: Fixed reading X10 images