Julia v0.5 compatibility + precompilation support

This new release adds :

• compatibility to the released Julia 0.5 version (but compatibility with 0.4 is abandoned)
• enables precompilation
• changes the API of rdiff : values for variables are no longer necessary, only types need to be provided. The package makes use of Julia's type inference to choose the differentiation rules instead of recalculating actual values of the whole graph. This should bring better performance, simpler code and open up new simplifications possibilities for the generated code.

julia 0.5 compatibility + new derivatives definitions

• restores compatibility with latest julia 0.5
• add derivatives definitions for :
  • tan, sinh, cosh, tanh,
  • asin, acos, atan,
  • round, ceil, floor, trunc, mod2pi,
  • log1p, expm1,
  • erf, erfc, gamma, lgamma, beta and lbeta

Add [ignore] keyword arg

New keyword argument to rdiff functions to indicate that one or several variables given as parameters do not need to be differentiated against.

bug fixes release

• removed pre-compilation that caused many problems (will come back after a more careful thinking)
• adaptation to julia v0.5 's getindex on scalar dimension #13612