[org_proj] review and update (#217)

* proof and theorem env

update proof and thm env

* Update orth_proj_thm2.tex

* Update orth_proj.md

* column notation

* update the thm and proof env

* fix proof env

* Update orth_proj.md

* Update orth_proj.md

* improve consistency and update code according to PEP8

* update figure and tex files

* relocate figure and tex

* Update lectures/orth_proj.md

Co-authored-by: Matt McKay <mmcky@users.noreply.github.com>

* Update orth_proj.md

* Update orth_proj.md

* fix previous prf environment due to nested math directive

* Update orth_proj.md

* Update lectures/orth_proj.md

* Update lectures/orth_proj.md

* update subtitles

---------

Co-authored-by: Humphrey Yang <u6474961@anu.edu.au>
Co-authored-by: Matt McKay <mmcky@users.noreply.github.com>
Co-authored-by: mmcky <mamckay@gmail.com>

Author: 3 people

lectures/_static/lecture_specific/orth_proj/orth_proj_thm2.pdf

@@ -19,12 +19,13 @@
     \draw[important line, thick]  (Z1) -- (O) node[right] {};
     \draw[important line, thick]  (Py) -- (Z2) node[right] {$S$};
     \draw[important line, blue,->]  (O) -- (y) node[right] {$y$};
+    \draw[important line, blue,->]  (O) -- (Py') node[anchor = north west, text width=5em] {$P y'$};
     \draw[dotted line] (0.54,0.27) -- (0.51,0.33);
     \draw[dotted line] (0.57,0.36) -- (0.51,0.33);
     \draw[dotted line] (-0.22,-0.11) -- (-0.25,-0.05);
     \draw[dotted line] (-0.31,-0.08) -- (-0.25,-0.05);
     \draw[dashed line, black] (y) -- (Py);
-    \draw[dashed line, black] (y') -- (Py') node[anchor = north west, text width=5em] {$P y'$};
+    \draw[dashed line, black] (y') -- (Py');
 \end{tikzpicture}
 
 \end{document}