graph tool supports skipping files

misc tweaks and additions

Changes:

* `gg.Union` always dedups elements, like `Uniq`.

Additions:

* Add `gg.Send`.
* Add `gg.Chan.Send`.
* Add `gg.Receive`.
* Add `gg.Chan.Receive`.
* Add `gg.GetStrict`.
* Add `gg.Slice.GetStrict`.

updates in `gg.LazyIniter`

Breaking:

* Remove `gg.LazyIniter.Ptr`.

Misc:

* Fix potential concurrency issues in `gg.LazyIniter`.
* Add `gg.LazyIniter.Clear`.
* Add `gg.LazyIniter.Reset`.

more slice functions, set methods, fixes

* Add `gg.Set.IsEmpty`.
* Add `gg.Set.IsNotEmpty`.
* Add `gg.TakeLastWhile`.
* Add `gg.Slice.TakeLastWhile`.
* Add `gg.DropLastWhile`.
* Add `gg.Slice.DropLastWhile`.
* Add `gg.FindLastIndex`.
* Add `gg.Slice.FindLastIndex`.
* Add `gg.FindLast`.
* Add `gg.Slice.FindLast`.
* Add `gg.FoundLast`.
* Add `gg.Slice.FoundLast`.
* Bugfix `gg.TakeWhile`.
* Bugfix `gg.DropWhile`.

add `gg.OrdMap`

better error tracing; breaking renaming; misc tweaks

Breaking:

* Rename `gg.JsonParse` → `gg.JsonDecode`.
* Rename `gg.JsonParseTo` → `gg.JsonDecodeTo`.
* Rename `gg.JsonParseCatch` → `gg.JsonDecodeCatch`.
* Rename `gg.Err.AppendStack` → `gg.Err.AppendStackTo`.
* Rename `gg.Trace.AppendIndent` → `gg.Trace.AppendIndentTo`.
* Rename `gg.Trace.AppendIndentTable` → `gg.Trace.AppendIndentTableTo`.
* Rename `gg.Trace.AppendIndentMulti` → `gg.Trace.AppendIndentMultiTo`.
* Rename `gg.Caller.AppendIndent` → `gg.Caller.AppendIndentTo`.
* Rename `gg.Caller.AppendNewlineIndent` → `gg.Caller.AppendNewlineIndentTo`.
* Rename `gg.Frames.AppendIndentTable` → `gg.Frames.AppendIndentTableTo`.
* Rename `gg.Frame.AppendIndent` → `gg.Frame.AppendIndentTo`.
* Rename `gg.Frame.AppendNewlineIndent` → `gg.Frame.AppendNewlineIndentTo`.
* Rename `gg.Frame.AppendRowIndent` → `gg.Frame.AppendRowIndentTo`.
* Rename `gtest.NoError` → `gtest.NoErr`.
* Rename `gtest.ErrorStr` → `gtest.ErrStr`.
* Rename `gtest.Err` → `gtest.VerbErr`.
* Rename `gtest.Error` → `gtest.Err`.

Other:

* Add `gg.JsonEncodeIndent`.
* Add `gg.JsonEncodeCatch`.
* Add `gg.JsonEncodeIndentCatch`.
* Add `gg.JsonDecodeOpt`.
* Add `gg.JsonDecodeOptTo`.
* Add `gg.StackAppenderTo`.
* Add `gg.WrapTracedAt`.
* Add `gg.TryTrans`.
* Add `gg.Compacted`.
* Add `gg.Split`.
* Add `gg.ReadDirFileNames`.
* Add `gg.Buf.AppendErrorStack`.
* Add `gg.Err.OwnTrace`.
* Add `gg.Errs.WrapTracedAt`.
* Add `gg.Trace.IsEmpty`.
* Add `gg.OrdSet.Reset`.
* Export more "msg X" functions in `gtest`.

minor additions in collection types, misc tweaks

* Add `gg.Coll.AddUniq`.
* Add `gg.LazyColl.AddUniq`.
* Better report in `gtest.Uniq`.

more slice funcs, better terminal clearing

* Revise terminal-clearing escape sequences.
* Add `gg.MapUniq`.
* Add `gg.MapFlatUniq`.
* Add `gg.Counts`.
* Add `gg.CountsInto`.
* Add `gg.UniqBy`.
* Rename `gg.TypeName` → `gg.TypeString`.

more comparison functions

* Add `gg.IsSorted`.
* Add `gg.Less2`.
* Add `gg.Less`.
* Add `gg.LessPrim2`.
* Add `gg.LessPrim`.
* Add `gg.LessEq2`.
* Add `gg.LessEq`.
* Add `gg.LessEqPrim2`.
* Add `gg.LessEqPrim`.
* Add `gg.AddUncheck`.
* Add `gg.SubUncheck`.
* Add `gg.Words.Piped`.
* Rename `gg.PtrSwap` → `gg.SnapSwap`.

Misc: move comparison and ptr funs to their own files.

`gsql`: avoid zeroing scan target

Previously, various scanning functions in `gsql`, specifically those
that take an addressable target, would always scan into a zero value,
then overwrite the target with the resulting value. This could cause
problems when the target contained non-DB fields not intended to be
zeroed, even when those fields were private.

The new behavior is to avoid allocating new values, unless appending
elements to slices, and prefer to scan into the provided addressable
target, avoiding the issue.