Code formatting and language feature additions to the style guide.

exception is when implementing logging since the benefits of readability

outweigh the cost of safety.

### Functions with zero arguments

Functions that do not take any arguments (0 arity) should be declared like so:

```

void function(void);

```

Note that the function explicitly includes `void` in its parameter list to

indicate to the compiler that it takes no arguments.

### Zero-length arrays

Use zero-length arrays as the last member of a struct if the array needs to be

allocated in contiguous memory with its containing struct. For example:

Instead, use zero-length arrays as described above to avoid pointer arithmetic

and array indexing entirely.

### Boolean type

Use the C99 `bool` type with values `true` and `false` defined in `stdbool.h`.

Not only is this a standardized type, it is also safer and provides more

compile-time checks.

## Header files

In general, every source file (`.c` or `.cpp`) in a `src/` directory should

have a corresponding header (`.h`) in the `include/` directory.

This form is used over traditional `#define`-based include guards as it is less

error-prone, doesn't pollute the global namespace, is more compact, and can

result in faster compilation.

## Formatting

Code formatting is pretty arbitrary, but the codebase is easier to follow if

everyone uses the same style. Individuals may not agree with every aspect of

the formatting rules, and some of the rules may take some getting used to,

but it is important that all engineers follow the formatting rules so we can all

understand and read the code easily.

### White space

* use only spaces, indent 2 spaces at a time

* no trailing whitespaces at the end of a line

* no tab characters

* use one blank line to separate logical code blocks, function definitions,

  and sections of a file

```

// Space after keyword in conditionals and loops.

// No space immeidately before or after parentheses.

if (foo)

// Space surrounding binary operators.

if (foo < 5)

// Space after comma.

for (int x = 0, y = 0; x; ++y)

// No space between unary operators and their argument.

++x;

z = -y;

// No space between function name and open parenthesis.

call_my_fn(arg1, arg2);

// Space before * in variable declaration.

int *x = NULL;

// Space after // beginning a comment.

// Notice the space between "//" and "N".

```

Use only spaces, and indent 2 spaces at a time. Do not use tab characters in the

codebase.

Use a single blank line to separate logical code blocks, function definitions,

and sections of a file.

### Brace style

```

// Open curly braces are never on a line by themselves.

void my_function(void) {

  // Conditional statements with only one child statement should elide braces.

  // The child statement must be on a new line, indented by 2 spaces.

  if (foo)

    do_bar();

  else

    do_baz();

  // Conditionals with a branch containing more than one child statement forces

  // braces on both branches.

  if (foo) {

    do_bar();

  } else {

    do_baz();

    ++var1;

  }

}

```