Added manul 4.1; opamp DIP8 SVG diagram and ALPACA diagrams PDF; remove obsolete requirements file

Author: zamkorus

book/_toc.yml

@@ -32,6 +32,8 @@ parts:
         sections:
           - file: manuals/week3/3.1_aliasing_and_anti_aliasing.ipynb
       - file: manuals/week4/_summary.ipynb
+        sections:
+          - file: manuals/week4/4.1_opamp_basics.ipynb
       - file: manuals/week5/_summary.ipynb
       - file: manuals/week6/_summary.ipynb
       - file: manuals/week7/_summary.ipynb