Issue Date before Expiry Date

[FuggeWolf]

• Throw error message if not(Issue Date < Expiry Date).
• Seek for consistency in the argument lists: currently we have - at least - the following inconsistency:

  BondSpecification(): ..., expiry_date, issue_date, ...
  InflationLinkedBondSpecification(): ..., issue_date, expiry_date, ...

[FuggeWolf]

There is another inconsistency between BondSpecification() and InflationLinkedBondSpecification():
While for the inflation linked bond a coupon schedule is provided, for bonds coupon dates and coupons, or reference index, coupon_periods and spreads have to be given, respectively.

[favdo]

Den 1sten Punkt habe ich gefixt.
2) Ich habe in der Schnittstelle beim Bond die Expiry und das Issue Date vertauscht, d.h. jetzt sollte es konsistent zum Inflation Linker sein.

[FuggeWolf]

to be tested by Stefan