doctests failing

[andreymlv]

Add main function with anyhow to doctests and create actual temp file or directory to pass tests.

Right now if call cargo test:

running 5 tests
test test::test_ls_file ... ok
test test::test_ls_dir ... ok
test test::test_ls_rec_file ... ok
test test::test_ls_rec_dir ... ok
test test::test_size ... ok

test result: ok. 5 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s


running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s


running 3 tests
test src/lib.rs - size (line 86) ... FAILED
test src/lib.rs - ls (line 12) ... FAILED
test src/lib.rs - ls_rec (line 46) ... FAILED

failures:

---- src/lib.rs - size (line 86) stdout ----
error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
 --> src/lib.rs:91:63
  |
4 | fn main() { #[allow(non_snake_case)] fn _doctest_main_src_lib_rs_86_0() {
  |                                      ---------------------------------- this function should return `Result` or `Option` to accept `?`
...
8 | let total_size = size(Path::new("/path/to/file_or_directory"))?;
  |                                                               ^ cannot use the `?` operator in a function that returns `()`
  |
  = help: the trait `FromResidual<Result<Infallible, anyhow::Error>>` is not implemented for `()`
help: consider adding return type
  |
4 ~ fn main() { #[allow(non_snake_case)] fn _doctest_main_src_lib_rs_86_0() -> Result<(), Box<dyn std::error::Error>> {
5 | use durs::size;
...
9 | println!("Total size: {} bytes", total_size);
10+     Ok(())
  |

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.
Couldn't compile the test.
---- src/lib.rs - ls (line 12) stdout ----
error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
 --> src/lib.rs:17:48
  |
4 | fn main() { #[allow(non_snake_case)] fn _doctest_main_src_lib_rs_12_0() {
  |                                      ---------------------------------- this function should return `Result` or `Option` to accept `?`
...
8 | let files = ls(Path::new("/path/to/directory"))?;
  |                                                ^ cannot use the `?` operator in a function that returns `()`
  |
  = help: the trait `FromResidual<Result<Infallible, anyhow::Error>>` is not implemented for `()`
help: consider adding return type
  |
4 | fn main() { #[allow(non_snake_case)] fn _doctest_main_src_lib_rs_12_0() -> Result<(), Box<dyn std::error::Error>> {
  |                                                                         +++++++++++++++++++++++++++++++++++++++++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.
Couldn't compile the test.
---- src/lib.rs - ls_rec (line 46) stdout ----
error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
 --> src/lib.rs:51:52
  |
4 | fn main() { #[allow(non_snake_case)] fn _doctest_main_src_lib_rs_46_0() {
  |                                      ---------------------------------- this function should return `Result` or `Option` to accept `?`
...
8 | let files = ls_rec(Path::new("/path/to/directory"))?;
  |                                                    ^ cannot use the `?` operator in a function that returns `()`
  |
  = help: the trait `FromResidual<Result<Infallible, anyhow::Error>>` is not implemented for `()`
help: consider adding return type
  |
4 | fn main() { #[allow(non_snake_case)] fn _doctest_main_src_lib_rs_46_0() -> Result<(), Box<dyn std::error::Error>> {
  |                                                                         +++++++++++++++++++++++++++++++++++++++++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0277`.
Couldn't compile the test.

failures:
    src/lib.rs - ls (line 12)
    src/lib.rs - ls_rec (line 46)
    src/lib.rs - size (line 86)

test result: FAILED. 0 passed; 3 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.02s