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.

streaming_algorithms/README.md

@@ -2,6 +2,6 @@
  
  [Counting large numbers of events in small registers](http://www.inf.ed.ac.uk/teaching/courses/exc/reading/morris.pdf) by Robert Morris
  
- [Probabilistic Counting Algorithms for Data Base Applications](https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=b36c153be410c0d937d7583de557c0375506d15a) by Philppe Flajolet, Nigel Martin
+ [Probabilistic Counting Algorithms for Data Base Applications](https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=b36c153be410c0d937d7583de557c0375506d15a) by Philippe Flajolet, Nigel Martin
  
  [The Space Complexity of Approximating the Frequency Moments](http://www.cs.ucsb.edu/~veronika/MAE/spacecomplexityapproxfreqmoments_alon_99.pdf) by Noga Alon, Yossi Matias, Mario Szegedy