widgets(table): implemented more header and column options

- Added the `HeaderNames` Type and `header_names` field to `TableContext` to let users choose between automatically getting header names from fields or setting custom names.
- Removed the `headers` parameter from `drawTable()`.
- Added the `ColumnIndexes` Type and `col_indexes` field to `TableContext` to let users choose which columns/fields they actually want to display.

examples/table.zig

···
     var demo_tbl: vaxis.widgets.Table.TableContext = .{
         .active_bg = active_bg,
         .selected_bg = selected_bg,
+        .header_names = .{ .custom = &.{ "First", "Last", "Username", "Email", "Phone#" } },
+        //.header_names = .{ .custom = &.{ "First", "Last", "Email", "Phone#" } },
+        //.col_indexes = .{ .by_idx = &.{ 0, 1, 3, 4 } },
         //.col_width = .{ .static_all = 15 },
         //.col_width = .{ .dynamic_header_len = 3 },
         //.col_width = .{ .static_individual = &.{ 10, 20, 15, 25, 15 } },
···
             try vaxis.widgets.Table.drawTable(
                 event_alloc,
                 middle_bar,
-                &.{ "First", "Last", "Username", "Email", "Phone#" },
                 //users_buf[0..],
                 user_list,
                 //user_mal,

src/widgets/Table.zig

···
     /// Note, if this is left `null` the Column Width will be dynamically calculated during `drawTable()`.
     //col_width: ?usize = null,
     col_width: WidthStyle = .dynamic_fill,
+    
+    // Header Names
+    header_names: HeaderNames = .field_names,
+    // Column Indexes
+    col_indexes: ColumnIndexes = .all,
 };
 
 /// Width Styles for `col_width`.
···
     static_individual: []const usize,
 };
 
+/// Column Indexes
+pub const ColumnIndexes = union(enum) {
+    /// Use all of the Columns.
+    all,
+    /// Use Columns from the specified indexes.
+    by_idx: []const usize,
+};
+
+/// Header Names
+pub const HeaderNames = union(enum) {
+    /// Use Field Names as Headers
+    field_names,
+    /// Custom
+    custom: []const []const u8,
+};
+
 /// Draw a Table for the TUI.
 pub fn drawTable(
     /// This should be an ArenaAllocator that can be deinitialized after each event call.
···
     alloc: ?mem.Allocator,
     /// The parent Window to draw to.
     win: vaxis.Window,
-    /// Headers for the Table
-    headers: []const []const u8,
     /// This must be a Slice, ArrayList, or MultiArrayList.
     /// Note, MultiArrayList support currently requires allocation.
     data_list: anytype,
···
     };
     defer if (di_is_mal) alloc.?.free(data_items);
 
+    // Headers for the Table
+    var hdrs_buf: [100][]const u8 = undefined;
+    const headers = hdrs: {
+        switch (table_ctx.header_names) {
+            .field_names => {
+                const DataT = @TypeOf(data_items[0]);
+                const fields = meta.fields(DataT);
+                var num_hdrs: usize = 0;
+                inline for (fields, 0..) |field, idx| contFields: {
+                    switch (table_ctx.col_indexes) {
+                        .all => {},
+                        .by_idx => |idxs| {
+                            if (mem.indexOfScalar(usize, idxs, idx) == null) break :contFields;
+                        },
+                    }
+                    num_hdrs += 1;
+                    hdrs_buf[idx] = field.name;
+                }
+                break :hdrs hdrs_buf[0..num_hdrs];
+           },
+            .custom => |hdrs| break :hdrs hdrs,
+        }
+    };
+
+
     const table_win = win.initChild(
         0,
         table_ctx.y_off,
···
         const DataT = @TypeOf(data);
         col_start = 0;
         const item_fields = meta.fields(DataT);
-        inline for (item_fields[0..], 0..) |item_field, item_idx| {
+        inline for (item_fields[0..], 0..) |item_field, item_idx| contFields: {
+            switch (table_ctx.col_indexes) {
+                .all => {},
+                .by_idx => |idxs| {
+                    if (mem.indexOfScalar(usize, idxs, item_idx) == null) break :contFields;
+                },
+            }
             const col_width = try calcColWidth(
                 item_idx,
                 headers,