strfmt: rust library for formatting dynamic strings

This library is for rust developers who want to bring rust-like formatting to non-static strings. For example, there is no way to do this:

let mut map = HashMap::new();
map.insert("name", "bob");
map.insert("job", "python developer");

// f contains "hi, my name is {name} and I am a {job}!"
let mut f = File::open("example.txt").unwrap();
let mut s = String::new();
f.read_to_string(&mut s).unwrap();

// prints "hi, my name is bob and I am a python developer!"
println!("{}", format(s, map));

This means that if you ever wanted to provide an interface where your user could use rust-style string formatting you were SOL -- well no more!

Scope

strfmt aims to support all of the formatting options defined in std::fmt that are useful for formatting strings and none of the options that are not useful for formatting strings.

Items in the stdlib syntax that strfmt will support (with comments on what isn't supported) are:

format_string := <text> [ format <text> ] *
format := '{' argument [ ':' format_spec ] '}'  # does not support empty `{}`
argument := identifier  # does not support integer

# format_spec does not support: sign, '#', 0, '.' precision or type
format_spec := [[fill]align][width]
fill := character
align := '<' | '^' | '>'
width := count
count := parameter | integer

Some notes:

• integer and empty {} are not supported because the formatter is always a HashMap<&str, &str> (dynamic types do not exist in rust like they do in python)
• type is not supported because it is always "s"
• sign, #, 0 and . are not supported because they are only related to numeric types