Fixed comment in TriangularDistribution example

The <summary> tag of the TriangularDistribution class read "ContinuousUniform distribution example". It now reads "Triangular distribution example".
ValidateMean unit test for Categorical dist

Unit tests to validate Categorical.Mean. Currently they fail, indicating
that Categorical.Mean is not correctly implemented.
Unit tests for StdDev, Variance, Entropy, and Median properties are
still required.
Fix to Categorical.Mean property.

Categorical.Mean was being calculated as _pmfNormalized.Mean(), which
 is actually the mean probability across all possible values, rather
 than the mean value of the distribution.
I've replaced it with a loop which performs the following standard
 calculation for mean value:

mean = Sum(x * f(x), x=0..N)
where f(x) is the probability mass function, and N is the maximum
 value.

An alternate method of calculation is:
 Mean = Sum( 1 - F(x), x=0..N) or similar[1].
That might be preferable if it results in less computational error,
 but it's a bit obscure, so for clarity I decided to go with the
 standard calculation for mean value.

[1]: https://en.wikipedia.org/w/index.php?title=Expected_value&oldid=585750484#Discrete_distribution_taking_only_non-negative_integer_values
Categorical dist: Tests for Var, SD, and Median

Added unit tests to validate the following properties of the
 Categorical distribution:
- Variance,
- StdDev, and
- Median.

TODO: Find out the expected behaviour of Median in ambiguous cases
 (e.g. where P(X=1)=0.5, and P(X=2)=0.5), then add appropriate unit
 tests.

TODO: Research how to calculate entropy, then add unit tests for the
 Entropy property.
Optimized the BigInteger parser function used when PORTABLE is defined; now, it doesn't create any intermediate strings via slicing.
Changed the BigRationalLarge type to a normal class instead of a single-case discriminated union because the F# compiler doesn't (yet) optimize single-case DU types as well as it could.
Removed the largely-unused BigRationalLargeImpl and BigRationalLarge modules; functions that were actually used were moved into members of the BigRationalLarge type.
Merge pull request #199 from jack-pappas/fs-bignum-optimized

BigNum Optimizations
- Added unit tests file for Triangular distribution (TriangularTests.cs).
- Added some unit tests for Triangular distribution, using BetaTests.cs as a template.
There are still more unit tests to bring over from BetaTests.cs.
- (fixed) Triangular dist's static sample methods weren't declared as static.
* To fix: Three of the existing tests are still failing.
Fixed unit test failure: Triangular should not accept infinite parameters.
I noticed that none of the other distribution classes check for infinite values, but perhaps they should.
See #201.
Note that +Infinity is a valid input parameter for the Beta distribution (see BetaTests.cs).
TriangularCreateFailsWithBadParameters is now a parameterised test with multiple test cases, instead of a single test containing multiple assertions.
File renames to comply with case sensitive file systems
fix build scripts to point to appropriate NuGet.exe on case sensitive file systems
Merge pull request #203 from smoothdeveloper/master

File renames to comply with case sensitive file systems
Distributions: static PMF, PMFLn, CDF functions for discrete distributions
Update release notes, contributors
LA: orthonormal basis of the kernel (null space) and range (column space)of a matrix. Nullity.
BigRational: add IsZero, IsOne, IsInteger, Reciprocal, Pow (compat with **), FromFraction
Modulus, Remainder and Factorial for BigInteger
Statistics: Median direct implementation instead of R8-compatible 0.5-quantile
Statistics: MeanStandardDeviation (analog to MeanVariance)