Added relation mathematical symbols

Added the following relation symbols listed in the link below that were
not already present.

http://en.wikibooks.org/wiki/LaTeX/Mathematics#List_of_Mathematical_Symbols

Added symbols:

`\ll\gg\sqsubset\sqsubseteq\sqsupset\sqsupseteq\prec\preceq\succ\succeq\doteq\equiv\simeq\sim\parallel\nparallel\perp\asymp\vdash\smile\frown\bowtie\dashv\ni\mid`