Documentation grammar and typo fixes (#174)
Documentation grammar and typo fixes (#174)

* Missing parameter in visibility function equation

The visibility function V_1 depends on l (or v) and alpha, but alpha was omitted in one equation.

* Fix typo its vs it is

* Fix typo usign -> using

* Fix typo algorightm -> algorithm

* Fix typo later -> latter

* Grammar: much less -> many fewer

* Fix missing equation label

Equation was referred to in the text, but did not have its label defined, causing the reference to show up as ???.

* Fix typo itentiy -> itentity

* Fix typo apperance -> appearance

* Fix typo participe -> participate

* Fix typo: scaterring -> scattering

* Consistency: grey -> gray

Since the document mostly uses American English, replace occurrences of "grey" (preferred spelling in UK) with "gray" (preferred spelling in US).

* Fix typo: interemdiate -> intermediate

* Fix typo: anistropic -> anisotropic

* Style: gaussian -> Gaussian

* Fix typo: particulary -> particularly

* Fix typo: subsitution -> substitution

* Fix typo: fomulate -> formulate

* Fix typo: evector -> vector

* Fix typo: tempetature -> temperature

* Fix typo: ar -> at

* Style: lambertian -> Lambertian

* Fix typo: disapears -> disappears

* Fix typo: acounting -> accounting

* Fix typo: simplificationss -> simplifications

* Fix typo: subsitute -> substitute

* Style: light saber -> lightsaber

* Fix typo: cooordinates -> coordinates

* Fix typo: probaility -> probability

* Fix typo: Hammersely -> Hammersley

* Fix typo: Mistuba -> Mitsuba

google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament,google/filament