combine functions behind to/from-c/tsv commands

fixes #969, admittedly without a --delimiter alias

moves from_structured_data.rs to from_delimited_data.rs to better
identify its scope and adds to_delimited_data.rs. Now csv and tsv both
use the same code, tsv passes in a fixed '\t' argument where csv passes
in the value of --separator

tests/filters_test.rs

@@ -129,6 +129,35 @@ fn converts_from_csv_text_with_separator_to_structured_table() {
     })
 }
 
+#[test]
+fn converts_from_csv_text_with_tab_separator_to_structured_table() {
+    Playground::setup("filter_from_csv_test_1", |dirs, sandbox| {
+        sandbox.with_files(vec![FileWithContentToBeTrimmed(
+            "los_tres_caballeros.txt",
+            r#"
+                first_name	last_name	rusty_luck
+                Andrés	Robalino	1
+                Jonathan	Turner	1
+                Yehuda	Katz	1
+            "#,
+        )]);
+
+        let actual = nu!(
+            cwd: dirs.test(), h::pipeline(
+            r#"
+                open los_tres_caballeros.txt
+                | from-csv --separator '\t'
+                | get rusty_luck
+                | str --to-int
+                | sum
+                | echo $it
+            "#
+        ));
+
+        assert_eq!(actual, "3");
+    })
+}
+
 #[test]
 fn converts_from_csv_text_skipping_headers_to_structured_table() {
     Playground::setup("filter_from_csv_test_2", |dirs, sandbox| {
@@ -267,6 +296,16 @@ fn can_convert_table_to_tsv_text_and_from_tsv_text_back_into_table() {
     assert_eq!(actual, "SPAIN");
 }
 
+#[test]
+fn can_convert_table_to_tsv_text_and_from_tsv_text_back_into_table_using_csv_separator() {
+    let actual = nu!(
+        cwd: "tests/fixtures/formats",
+        r"open caco3_plastics.tsv | to-tsv | from-csv --separator '\t' | first 1 | get origin | echo $it"
+    );
+
+    assert_eq!(actual, "SPAIN");
+}
+
 #[test]
 fn converts_structured_table_to_tsv_text() {
     Playground::setup("filter_to_tsv_test_1", |dirs, sandbox| {