Generic linear solver for upper triangular matrices

- Generic inverse replaced with generic solve on identity matrix
- Specialized transpose, ctranspose, istril, istriu
Provides cond(A::Triangular)

- wraps LAPACK wrapper trcon!, reciprocal of condition number estimate for triangular matrices
- type stability bugfixes to generic cond()
- Triangular-specific tests for linear solver and cond()
Provide eigvals(A::Triangular)
Provides methods and tests for eigvecs, eigfact
Update News.md
Provides eigenvector computations
- Wraps LAPACK.trevc!
- New eigvecs{T<:BlasFloat}(A::Triangular{T}) method
Specialized routines for Triangular matrices

Addresses #3688

- Provides diag, generic multiplication and other simple routines
- Eigensystem solvers: eigvals, eigvecs, eigfact
- Provides simple wrappers for singular system solvers
- Adds convert routine from Triangular to dense Matrix
- Clean up bidiagonal Matrix tests
Generic linear solve for dense matrices respects real/complex difference
Add more Triangular tests
- Tests BigFloat and Complex{BigFloat}
- Tests naive substitution solver for all float types
Provides big(A::Triangular)
Comment out tests for nonexistent bidiagonal eigensolvers (moved to new branch)
Triangular solver now checks for unreasonably large errors in solution

- Wraps LAPCK.trrfs! which computes forward and backward errors