Added initial part of the user guide.
create the class to groupby Summary
Merge pull request #38 from otaviojava/group_by_currency_summary

create the class to groupby Summary
Changed parent to 0.5.
Added rounding to some operator implementations.
Fixed reciprocal.
Updated Java Docs, headers.
Further improved user guide.
Updated user guide.
Updated gitignore
https://java.net/jira/browse/JAVAMONEY-75 :
Unified getCurrency/setCurrency method names.
Adapted to this change.
Merge branch 'master' of https://github.com/JavaMoney/jsr354-ri
https://java.net/jira/browse/JAVAMONEY-77
Replaced create() with of() in builders.
Removed exposure of BuildableCurrencyUnit and DefaultExchangeRate in RI by refactoring builder pattern similar to RI.
Fixed pom changed by refactoring!
Moved ServicePriority to SPI.
Added private constructor to CurrencyUnitBuilder.
Updated user guide.