Various issues with the documentation

[gvalentini85]

List of various issues I found in the documentation of inform while developing the R wrapper (rinform):

• many time series measures point to a wiki page, Transfer Entropy lacks this link although there is a wiki page (https://en.wikipedia.org/wiki/Transfer_entropy)
• transfer entropy: "between an information source and destination" -> missing "a destination"
• transfer entropy: "interest have more just those two" -> missing "more than"
• around the whole documentation: links to the inform github are sometimes broken, e.g. the "yet!" link https://github.com/elife-asu/issues/24 should be Extrapolating to Infinite History Lengths #24
• predictive info, examples: "between a the current time step" should be "between the current time step"
• the following ref is missing the journal name: "[Hoel2017] Hoel, E.P. (2017) "When the map is better than the territory". 19 (5): 188. doi:10.3390/e19050188."
• reference [Ay2008] is not defined in the documentation
• equations for entropy rate is missing a negative sign