Move optimization routines to git

[jarlebring]

The dropbox function opt_gaussnewton! needs to be moved into git.

• [x] Function documentation (all kwargs and retvals should be mentioned )
• [x] unit tests
• [x] clean up (e.g. remove unneccessary j=1?)
• [x] remove artificial_condition functionality (it was used before we realized how bigfloat svd should be used)
• [x] Proposal: Make function adjust_for_errtype! adjust both R and Jac with one call. Seems more natural than making two calls.
• [x] Proposal: Make objfun a mandatory arg rather than a kwarg. It is so central that I don't see convenience in having a default value.

[eringh]

a38467a0be2256b220137148058a4424c09b7362 and c7e9ac2071b73c3086e68f33be85fa96eaa430c1