Bit flags

Short bit flags description

This is an example, using a 8-bit unsigned integer to store 8 flags:
 
`unsigned char options;`

It is common to use larger fields, e.g. 32 bits, but I use 8 here for simplicity.

The possible options, that can be turned on or off independently are declared in an enum like this (just using some arbitrary identifiers):
```
enum Options {
  OpAutoRedraw    = 0x01,
  OpAntiAlias     = 0x02,
  OpPixelShader   = 0x04,
  OpVertexShader  = 0x08,
  OpFullscreen    = 0x10,
  OpDaylight      = 0x20
  // ...
};
```

Note how each option is given a specific value. These values are carefully picked to match each bit in the 8-bit variable:
```
// 0x01 ==   1 == "00000001"
// 0x02 ==   2 == "00000010"
// 0x04 ==   4 == "00000100"
// 0x08 ==   8 == "00001000"
// 0x10 ==  16 == "00010000"
// 0x20 ==  32 == "00100000"
// 0x40 ==  64 == "01000000"
// 0x80 == 128 == "10000000" 
```
Now, each flag can be set independently, by using the bitwise OR operator:
```
options = OpAutoRedraw | OpVertexShader | OpFullscreen;
// options == 0x01 | 0x08 | 0x10 == "00011001" 
```

And can be tested using the bitwise AND operator:
```
if (options & OpAutoRedraw) {} // true
if (options & OpAntiAlias) {} // false 
```

I hope this helps!