DOC: Add NEP45 and NEP29 targets, use <NEPxx> links

Per gh-16500, changed link style to :ref:`<NEPxx>`.

Added a NEP45 target to NEP 45, and added a NEP29 target
to NEP 29 since it has the irregular NEP0029 target.

The two new NEP targets aren't picked up, though the
older ones are. Tried make clean in neps and docs.

```
  /home/bjn/numpy_git/numpy-1/doc/source/dev/index.rst:191: WARNING: undefined label: nep45 (if the link has no caption the label must precede a section header)
  HOWTO_RELEASE.rst.txt:43: WARNING: undefined label: nep29 (if the link has no caption the label must precede a section header)
  HOWTO_RELEASE.rst.txt:50: WARNING: undefined label: nep29 (if the link has no caption the label must precede a section header)
```

The nep objects.inv does seem to have both the nep29 and nep44 targets.

5 files changed, 9 insertions, 9 deletions

diff --git a/doc/HOWTO_RELEASE.rst.txt b/doc/HOWTO_RELEASE.rst.txt
index c3abbfde3..d5abd2c92 100644
--- a/doc/HOWTO_RELEASE.rst.txt
+++ b/doc/HOWTO_RELEASE.rst.txt
@@ -40,7 +40,7 @@ Release Scripts
 
 Supported platforms and versions
 ================================
-:doc:`NEP 29<neps:nep-0029-deprecation_policy>` outlines which Python versions
+:ref:`NEP 29 <NEP29>` outlines which Python versions
 are supported; For the first half of 2020, this will be Python >= 3.6. We test
 NumPy against all these versions every time we merge code to master.  Binary
 installers may be available for a subset of these versions (see below).
@@ -48,7 +48,7 @@ installers may be available for a subset of these versions (see below).
 OS X
 ----
 OS X versions >= 10.9 are supported, for Python version support see
-:doc:`NEP 29<neps:nep-0029-deprecation_policy>`. We build binary wheels for
+:ref:`NEP 29 <NEP29>`. We build binary wheels for
 OSX that are compatible with Python.org Python, system Python, homebrew and
 macports - see this `OSX wheel building summary
 <https://github.com/MacPython/wiki/wiki/Spinning-wheels>`_ for details.
diff --git a/doc/neps/nep-0029-deprecation_policy.rst b/doc/neps/nep-0029-deprecation_policy.rst
index 9b6022a81..dbead1b9b 100644
--- a/doc/neps/nep-0029-deprecation_policy.rst
+++ b/doc/neps/nep-0029-deprecation_policy.rst
@@ -1,4 +1,4 @@
-.. _NEP0029:
+.. _NEP29:
 
 ==================================================================================
 NEP 29 — Recommend Python and Numpy version support as a community policy standard
diff --git a/doc/neps/nep-0045-c_style_guide.rst b/doc/neps/nep-0045-c_style_guide.rst
index fb898dfed..d7fa6fd97 100644
--- a/doc/neps/nep-0045-c_style_guide.rst
+++ b/doc/neps/nep-0045-c_style_guide.rst
@@ -1,3 +1,5 @@
+.. _NEP45:
+
 =================================
 NEP 45 — C Style Guide
 =================================
@@ -244,7 +246,7 @@ C functions, see the files in ``doc/cdoc/``.
 Related Work
 ------------
 
-Based on Van Rossum and Warsaw, :pep:`7`_
+Based on Van Rossum and Warsaw, :pep:`7`
 
 
 Discussion
diff --git a/doc/source/dev/howto-docs.rst b/doc/source/dev/howto-docs.rst
index d9955ddae..c1f63bbef 100644
--- a/doc/source/dev/howto-docs.rst
+++ b/doc/source/dev/howto-docs.rst
@@ -36,8 +36,7 @@ Current vision for the documentation: NEP 44
 
 Recently, the NumPy community approved a *NumPy Enhancement Proposal (NEP)*
 about documentation,
-:doc:`NEP 44 - Restructuring the NumPy Documentation
-     <neps:nep-0044-restructuring-numpy-docs>`.
+:ref:`NEP 44 - Restructuring the NumPy Documentation <NEP44>`.
 
 **Where is the documentation?**
 
diff --git a/doc/source/dev/index.rst b/doc/source/dev/index.rst
index 6f04e0bc0..1a34885c4 100644
--- a/doc/source/dev/index.rst
+++ b/doc/source/dev/index.rst
@@ -140,8 +140,7 @@ Here's the short summary, complete TOC links are below:
 
    If your change introduces a deprecation, make sure to discuss this first on
    GitHub or the mailing list first. If agreement on the deprecation is
-   reached, follow `NEP 23 deprecation policy <http://www.numpy.org/neps/
-   nep-0023-backwards-compatibility.html>`_  to add the deprecation.
+   reached, follow :ref:`NEP 23 deprecation policy <NEP23>`  to add the deprecation.
 
 6. Cross referencing issues
 
@@ -189,7 +188,7 @@ Stylistic Guidelines
 
    import numpy as np
 
-* For C code, see `NEP 45 <https://numpy.org/neps/nep-0045-c_style_guide.html>`_.
+* For C code, see :ref:`NEP 45 <NEP45>`.
 
 
 Test coverage