readme: Turn package references into links

For base functionality we have overview in the readme itself, but for
packages we have only their listing with brief overview and no
documentation for in-package functionality.

Let's have at least links to .h/.pxd/.py where package functionality is
documented.

README.rst

@@ -328,14 +328,30 @@ Concurrency
 In addition to `go` and channels, the following packages are provided to help
 handle concurrency in structured ways:
 
-- `golang.context` provides contexts to propagate deadlines, cancellation and
+- |golang.context|_ (py__, pyx__) provides contexts to propagate deadlines, cancellation and
   task-scoped values among spawned goroutines [*]_.
 
-- `golang.sync` provides `sync.WorkGroup` to spawn group of goroutines working
+  .. |golang.context| replace:: `golang.context`
+  .. _golang.context: https://lab.nexedi.com/kirr/pygolang/tree/master/golang/context.h
+  __ https://lab.nexedi.com/kirr/pygolang/tree/master/golang/context.py
+  __ https://lab.nexedi.com/kirr/pygolang/tree/master/golang/_context.pxd
+
+- |golang.sync|_ (py__, pyx__) provides `sync.WorkGroup` to spawn group of goroutines working
   on a common task. It also provides low-level primitives - for example
   `sync.Once`, `sync.WaitGroup` and `sync.Mutex` - that are sometimes useful too.
 
-- `golang.time` provides timers integrated with channels.
+  .. |golang.sync| replace:: `golang.sync`
+  .. _golang.sync: https://lab.nexedi.com/kirr/pygolang/tree/master/golang/sync.h
+  __ https://lab.nexedi.com/kirr/pygolang/tree/master/golang/sync.py
+  __ https://lab.nexedi.com/kirr/pygolang/tree/master/golang/_sync.pxd
+
+- |golang.time|_ (py__, pyx__) provides timers integrated with channels.
+
+  .. |golang.time| replace:: `golang.time`
+  .. _golang.time: https://lab.nexedi.com/kirr/pygolang/tree/master/golang/time.h
+  __ https://lab.nexedi.com/kirr/pygolang/tree/master/golang/time.py
+  __ https://lab.nexedi.com/kirr/pygolang/tree/master/golang/_time.pxd
+
 
 .. [*] See `Go Concurrency Patterns: Context`__ for overview.
 
@@ -354,9 +370,12 @@ without escaping printable UTF-8 characters::
 `qq` accepts both `str` and `bytes` (`unicode` and `str` on Python2)
 and also any other type that can be converted to `str`.
 
-Package `golang.strconv` provides direct access to conversion routines, for
+Package |golang.strconv|_ provides direct access to conversion routines, for
 example `strconv.quote` and `strconv.unquote`.
 
+.. |golang.strconv| replace:: `golang.strconv`
+.. _golang.strconv: https://lab.nexedi.com/kirr/pygolang/tree/master/golang/strconv.py
+
 
 Benchmarking and testing
 ~~~~~~~~~~~~~~~~~~~~~~~~
@@ -378,13 +397,17 @@ gives something like::
     Benchmarkadd    50000000        0.020 µs/op
     Benchmarkadd    50000000        0.020 µs/op
 
-Package `golang.testing` provides corresponding runtime bits, e.g. `testing.B`.
+Package |golang.testing|_ provides corresponding runtime bits, e.g. `testing.B`.
 
 `py.bench` produces output in `Go benchmark format`__, and so benchmark results
 can be analyzed and compared with standard Go tools, for example with
 `benchstat`__.
-Additionally package `golang.x.perf.benchlib` can be used to load and process
+Additionally package |golang.x.perf.benchlib|_ can be used to load and process
 such benchmarking data in Python.
 
+.. |golang.testing| replace:: `golang.testing`
+.. _golang.testing: https://lab.nexedi.com/kirr/pygolang/tree/master/golang/testing.py
+.. |golang.x.perf.benchlib| replace:: `golang.x.perf.benchlib`
+.. _golang.x.perf.benchlib: https://lab.nexedi.com/kirr/pygolang/tree/master/golang/x/perf/benchlib.py
 __ https://github.com/golang/proposal/blob/master/design/14313-benchmark-format.md
 __ https://godoc.org/golang.org/x/perf/cmd/benchstat