Fix Clippy warnings

[samford]

This fixes the following Clippy warnings:

warning: using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`
  --> components/front_matter/src/page.rs:90:17
   |
90 |                 DateTime::parse_from_rfc3339(&d).ok().and_then(|s| Some(s.naive_local()))
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try this: `DateTime::parse_from_rfc3339(&d).ok().map(|s| s.naive_local())`
   |
   = note: `#[warn(clippy::option_and_then_some)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#option_and_then_some

warning: using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`
  --> components/front_matter/src/page.rs:92:17
   |
92 | /                 NaiveDate::parse_from_str(&d, "%Y-%m-%d")
93 | |                     .ok()
94 | |                     .and_then(|s| Some(s.and_hms(0, 0, 0)))
   | |___________________________________________________________^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#option_and_then_some
help: try this
   |
92 |                 NaiveDate::parse_from_str(&d, "%Y-%m-%d")
93 |                     .ok().map(|s| s.and_hms(0, 0, 0))
   |

warning: useless use of `format!`
   --> components/library/src/pagination/mod.rs:193:13
    |
193 |             format!("{}", self.permalink)
    |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using .to_string(): `self.permalink.to_string()`
    |
    = note: `#[warn(clippy::useless_format)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#useless_format

I did not address the following Clippy warning, since it requires more architectural changes and I didn't want to make a decision on how to best approach it:

warning: this function has too many arguments (8/7)
   --> src/cmd/serve.rs:147:1
    |
147 | / pub fn serve(
148 | |     interface: &str,
149 | |     port: u16,
150 | |     output_dir: &str,
...   |
155 | |     include_drafts: bool,
156 | | ) -> Result<()> {
    | |_______________^
    |
    = note: `#[warn(clippy::too_many_arguments)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#too_many_arguments

[Keats]

Thanks!