contracts/chequebook: add chequebook contract wrapper

The wrapper code is adapted from the swarm/services/chequebook package
with the following mostly cosmetic changes:

* The code now uses the new Go API interfaces to query balances. Some
  minor functional changes were required to make this work.
* The package no longer depends on swarm/services/swap/swap. References
  to swap.Promise are replaced by interface{}, the base type of Promise.
  This is temporary.
* The contract wrapper has been regenerated with latest abigen
  and solc v0.3.6.
* There is a new generator that creates the 'deployed code' variable.
* Documentation comments now follow the recommended godoc style.
* [CHEQUEBOOK] log prefixes are gone.
* LGPL license headers have been added to all files.

contracts/chequebook/api.go

@@ -0,0 +1,68 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package chequebook
+
+import (
+	"errors"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+)
+
+const Version = "1.0"
+
+var errNoChequebook = errors.New("no chequebook")
+
+type Api struct {
+	chequebookf func() *Chequebook
+}
+
+func NewApi(ch func() *Chequebook) *Api {
+	return &Api{ch}
+}
+
+func (self *Api) Balance() (string, error) {
+	ch := self.chequebookf()
+	if ch == nil {
+		return "", errNoChequebook
+	}
+	return ch.Balance().String(), nil
+}
+
+func (self *Api) Issue(beneficiary common.Address, amount *big.Int) (cheque *Cheque, err error) {
+	ch := self.chequebookf()
+	if ch == nil {
+		return nil, errNoChequebook
+	}
+	return ch.Issue(beneficiary, amount)
+}
+
+func (self *Api) Cash(cheque *Cheque) (txhash string, err error) {
+	ch := self.chequebookf()
+	if ch == nil {
+		return "", errNoChequebook
+	}
+	return ch.Cash(cheque)
+}
+
+func (self *Api) Deposit(amount *big.Int) (txhash string, err error) {
+	ch := self.chequebookf()
+	if ch == nil {
+		return "", errNoChequebook
+	}
+	return ch.Deposit(amount)
+}