Add simple configuration file

This allows users to create simple configuration file
(`~/.config/bat/config` on Linux) that has the following format:

    ```bash
    --flag1
    --flag2
    --option1=value1
    # lines beginning with '#' are ignored
    --option2=value2
    # empty lines and trailing whitespace are also ignored

    --option3=value3
    ```

src/dirs.rs

@@ -0,0 +1,6 @@
+use directories::ProjectDirs;
+
+lazy_static! {
+    pub static ref PROJECT_DIRS: ProjectDirs =
+        ProjectDirs::from("", "", crate_name!()).expect("Could not get home directory");
+}