README and NEWS overhaul

Author: willtebbutt

NEWS.md

@@ -0,0 +1,8 @@
+- From v0.6.0, Libtask is implemented by recording all the computing
+  to a tape and copying that tape. Before that version, it is based on
+  a tricky hack on the Julia internals. You can check the commit
+  history of this repo to see the details.
+
+- From version 0.9.0, the old `TArray` and `TRef` types are completely removed, where
+  previously they were only deprecated. Additionally, the internals have been completely
+  overhauled, and the public interface more precisely defined. See the docs for more info.

README.md

@@ -2,100 +2,8 @@
 
 [![Libtask Testing](https://github.com/TuringLang/Libtask.jl/workflows/Libtask%20Testing/badge.svg)](https://github.com/TuringLang/Libtask.jl/actions?branch=master)
 
-Tape based task copying in Turing
 
-## Getting Started
+Resumable and copyable functions in Julia, with optional dynamic scope.
+See the docs for example usage.
 
-Stack allocated objects are always deep copied:
-
-```julia
-using Libtask
-
-function f()
-  t = 0
-  for _ in 1:10
-    produce(t)
-    t = 1 + t
-  end
-end
-
-ttask = TapedTask(f)
-
-@show consume(ttask) # 0
-@show consume(ttask) # 1
-
-a = copy(ttask)
-@show consume(a) # 2
-@show consume(a) # 3
-
-@show consume(ttask) # 2
-@show consume(ttask) # 3
-```
-
-Heap-allocated Array and Ref objects are deep copied by default:
-
-```julia
-using Libtask
-
-function f()
-  t = [0 1 2]
-  for _ in 1:10
-    produce(t[1])
-    t[1] = 1 + t[1]
-  end
-end
-
-ttask = TapedTask(f)
-
-@show consume(ttask) # 0
-@show consume(ttask) # 1
-
-a = copy(ttask)
-@show consume(a) # 2
-@show consume(a) # 3
-
-@show consume(ttask) # 2
-@show consume(ttask) # 3
-```
-
-Other heap-allocated objects (e.g., `Dict`) are shallow copied, by default:
-
-```julia
-using Libtask
-
-function f()
-  t = Dict(1=>10, 2=>20)
-  while true
-    produce(t[1])
-    t[1] = 1 + t[1]
-  end
-end
-
-ttask = TapedTask(f)
-
-@show consume(ttask) # 10
-@show consume(ttask) # 11
-
-a = copy(ttask)
-@show consume(a) # 12
-@show consume(a) # 13
-
-@show consume(ttask) # 14
-@show consume(ttask) # 15
-```
-
-Notes:
-
-- The [Turing](https://github.com/TuringLang/Turing.jl) probabilistic
-  programming language uses this task copying feature in an efficient
-  implementation of the [particle
-  filtering](https://en.wikipedia.org/wiki/Particle_filter) sampling
-  algorithm for arbitrary order [Markov
-  processes](https://en.wikipedia.org/wiki/Markov_model#Hidden_Markov_model).
-
-- From v0.6.0, Libtask is implemented by recording all the computing
-  to a tape and copying that tape. Before that version, it is based on
-  a tricky hack on the Julia internals. You can check the commit
-  history of this repo to see the details.
-
-- From version 0.9.0, the old `TArray` and `TRef` types are completely removed, where previously they were deprecated.
+Used in the [Turing](https://github.com/TuringLang/Turing.jl) probabilistic programming language to implement various particle-based inference methods, for example those in [AdvancedPS.jl](https://github.com/TuringLang/AdvancedPS.jl/).