updates: create BMP capabilities, bytes alignment, un-typecast malloc, handle argv

details,
1. added better argv handling method by using array key: BITMAP_FILE, SECRET_TEXT
2. updated `t_bitmap *create_bitmap()' function, and create a plain color bitmap
3. added test create bitmap function - `void test_create_bitmap()'
4. added write bitmap object to file function - `size_t write_bitmap_file()'
5. added helper method to write bitmap pixel storage (with padding bytes alignment)
         ^^^^^^^^^^^^^
         size_t write_bitmap_pixel_data(t_bitmap *, FILE *);
6. added `get_rowsize()' function to get total row size in bytes required
7. added `get_pixel_array_size()' function to get total pixel storage size required
8. added `padding_check()' function to check for padding bytes required
9. eliminated typecast for malloc return value, it's not required in C