[feat] Add set_enable_paris_formatting() ConfigBuilder method to control whether…

[shimaowo]

… a given logger uses or strips paris formatting. Only available with the paris feature, defaults to enabled for backwards compatibility. Fixes #98 and #112

This basically just defers the paris formatting until actual log time, rather than having it applied as part of the initial macro. This allows specifying different values per-logger (via their Config), which can then be passed to the new paris method.

paris_macros was removed as it is no longer used.

I chose to add a new flag, rather than use write_log_enable_colors, as the setter for that is already gated by the ansi_term feature, and presumably already has a use.

The extra 'return' is due to rust not understanding that a terminating statement is an implicit return if there is a later #[cfg] block.

I did not include a test as there are no paris tests currently.

Simple example:

use log::*;
use simplelog::*;
use std::fs::File;

fn main() {
    CombinedLogger::init(vec![
        TermLogger::new(
            LevelFilter::Info,
            Config::default(),
            TerminalMode::Mixed,
            ColorChoice::Auto),

        WriteLogger::new(
            LevelFilter::Debug,
            ConfigBuilder::new()
                .set_enable_paris_formatting(false)
                .build(),
            File::create("log.txt").unwrap()
        )
    ]).unwrap();

    info!("Here is some <blue>colored</> text.");
}

The TermLogger output will be colored as usual; the WriteLogger output will simply be the message "Here is some colored text." with no markup or formatting.

[shimaowo]

@Drakulix So the tests fail this way even in master, due to the discrepancy between how the log import is handled. I could try to address that here, but it's kind of orthogonal.

[shimaowo]

Actually this is easier to fix with this changeset than it is in master, because paris no longer requires special handling.

This PR will go through one of these days!