feat: add tryfiles

[1lann]

This PR adds a tryfiles directive to make it easier to serve compiled static content (React, Vue, etc.) for single page/progressive web apps or whatever you call them.

The default configuration (i.e. you only specify tryfiles and nothing else) looks like this:

# files to try in order
tryfiles {path} index.html index.htm index.txt default.html default.htm default.txt {
    # specify paths to exclude from this rule
    except /.well-known {cfg.addr.path}/.well-known
    # specify path prefixes to strip before trying to find them on the filesystem.
    without {cfg.addr.path}
}

where {cfg.addr.path} refers to the configured host's path if it is hosted on a subpath. For example:

chuie.io/example {
    # server config
}

# {cfg.addr.path} == "/example"

I also fixed some annoying bullshit like how the built in handler would redirect index.html permanently??? which imo is kinda ass. Now it doesn't attempt to redirect index.html at all, and it will only use temporary redirects.

@Lustyn @emmachase lmk what you think and if this covers your/all needs

Resolves #10

[emmachase]

Looks great