DOC: fixed Ricker wavelet formula
DOC: fixed Ricker wavelet formula

- equations are one-lined in website documentation, making the
  formula false by the absence of parenthesis in denominators;
- to follow the convention from other docstrings, exponentiation is put
  in Python-formatted form instead of LaTeX one;
- in the same spirit, implicit multiplication is avoided,
  and some other minor changes are made for cosmetic purposes;

vigna/scipy,aeklant/scipy,vigna/scipy,jamestwebber/scipy,vigna/scipy,person142/scipy,pizzathief/scipy,anntzer/scipy,anntzer/scipy,matthew-brett/scipy,endolith/scipy,tylerjereddy/scipy,mdhaber/scipy,nmayorov/scipy,WarrenWeckesser/scipy,tylerjereddy/scipy,arokem/scipy,grlee77/scipy,arokem/scipy,perimosocordiae/scipy,arokem/scipy,matthew-brett/scipy,andyfaff/scipy,nmayorov/scipy,mdhaber/scipy,rgommers/scipy,Eric89GXL/scipy,andyfaff/scipy,arokem/scipy,grlee77/scipy,perimosocordiae/scipy,perimosocordiae/scipy,perimosocordiae/scipy,scipy/scipy,nmayorov/scipy,Eric89GXL/scipy,e-q/scipy,andyfaff/scipy,Eric89GXL/scipy,e-q/scipy,WarrenWeckesser/scipy,zerothi/scipy,vigna/scipy,e-q/scipy,andyfaff/scipy,pizzathief/scipy,aeklant/scipy,tylerjereddy/scipy,aeklant/scipy,zerothi/scipy,jamestwebber/scipy,zerothi/scipy,ilayn/scipy,mdhaber/scipy,tylerjereddy/scipy,Stefan-Endres/scipy,anntzer/scipy,perimosocordiae/scipy,mdhaber/scipy,ilayn/scipy,Eric89GXL/scipy,endolith/scipy,andyfaff/scipy,endolith/scipy,andyfaff/scipy,mdhaber/scipy,aeklant/scipy,scipy/scipy,endolith/scipy,ilayn/scipy,rgommers/scipy,grlee77/scipy,matthew-brett/scipy,pizzathief/scipy,mdhaber/scipy,WarrenWeckesser/scipy,e-q/scipy,ilayn/scipy,scipy/scipy,jamestwebber/scipy,tylerjereddy/scipy,ilayn/scipy,Eric89GXL/scipy,scipy/scipy,rgommers/scipy,matthew-brett/scipy,aeklant/scipy,anntzer/scipy,endolith/scipy,scipy/scipy,jamestwebber/scipy,vigna/scipy,zerothi/scipy,ilayn/scipy,WarrenWeckesser/scipy,e-q/scipy,person142/scipy,Stefan-Endres/scipy,rgommers/scipy,jamestwebber/scipy,Stefan-Endres/scipy,zerothi/scipy,WarrenWeckesser/scipy,person142/scipy,grlee77/scipy,nmayorov/scipy,pizzathief/scipy,Stefan-Endres/scipy,anntzer/scipy,Stefan-Endres/scipy,nmayorov/scipy,arokem/scipy,rgommers/scipy,Stefan-Endres/scipy,grlee77/scipy,pizzathief/scipy,scipy/scipy,person142/scipy,anntzer/scipy,WarrenWeckesser/scipy,perimosocordiae/scipy,Eric89GXL/scipy,matthew-brett/scipy,endolith/scipy,zerothi/scipy,person142/scipy