reduce temporary allocations in Color serde impl

[kristopherbullinger]

hello. i have made some small changes in the impl of Serialize and Deserialize for crossterm::style::Color which reduces the number of temporary allocations created. To achieve this, I have:

• replaced calls to str::replace with other suitable methods such as str::strip_{suffix|prefix} in the deserialize impl
• replaced a collected-into vec with manually polling an iterator 4 times and applying pattern matching in the deserialize impl
• used a stack-based string for formatting ansi and rgb strings instead of the string-based format! macro

For ease of implementation, I have brought in the arrayvec dependency, dependent on the serde crossterm feature. This enables using the write! macro on an arrayvec::ArrayString rather than fiddling with an array on the stack and having to uphold utf8 invariants manually. The length of the stack-based string is based on the longest possible formatted color, which is "rgb_(255,255,255)", at length 17.

The deserialize tests as written are all still passing, and a manual check of the serialize impls confirms that colors Color::Rgb{ r: 255, g: 255, b: 255 }, Color::Ansi(1), and Color::Red still serialize as expected (debug printing shown):

Ok("\"rgb_(255,255,255)\"")
Ok("\"ansi_(1)\"")
Ok("\"red\"")