Fix broken hosted-paper link and typos in topic READMEs (#894)

* Fix broken hosted-paper link and typos in topic READMEs

The FRP index links the hosted paper as
[Deprecating the Observer Pattern](deprecating-the observer-pattern.pdf).
The file on disk really is named with a space, but an unescaped space is not
allowed in a CommonMark link destination, so the entry renders as literal text
instead of a link. Percent-encode the space so it resolves to the committed PDF.

Also correct misspellings in paper titles and descriptions:

- Algorithims -> Algorithms (comp_sci_fundamentals_and_history)
- simplifed -> simplified (data_structures)
- sucessful -> successful, numberator -> numerator,
  demoninator -> denominator, authoratitative -> authoritative
  (information_retrieval)
- Expresions -> Expressions (logic_and_programming)
- represention -> representation (mathematics)
- Probablistic -> Probabilistic (robotics, sublinear_algorithms)
- Philppe -> Philippe (streaming_algorithms)

* Rename the Deprecating the Observer Pattern PDF to drop the space

Per review, renaming the file rather than percent-encoding the link.

mathematics/README.md

@@ -14,7 +14,7 @@
 
   The *graph isomorphism problem* shows how to construct graphs using a simple building-block ("basis"). The same method applies to finding different building blocks to construct the same things. This technique can be applied to file systems, greplin, trees, virtual DOM, etc.
 
-  A short paper, it also shows how to use `𝔰𝔩₂(ℂ)` as a simple mathematical object that leads into the area of real mathematics—represention theory.
+  A short paper, it also shows how to use `𝔰𝔩₂(ℂ)` as a simple mathematical object that leads into the area of real mathematics—representation theory.
 
 * [Conway's ZIP proof](https://www.maths.ed.ac.uk/~v1ranick/papers/francisweeks.pdf) by George Francis and Jeffrey Weeks